Introduction to Biology By

Emily Lain

Reviewed by

Tessa Scrobola

About the Author

Emily J. Lain has a Master of Science degree in Biological Sciences from the University of Southern Mississippi in Hattiesburg, Mississippi, and a Bachelor of Science degree in Forestry from the University of Wisconsin-Stevens Point. During the pursuit of her degrees, Ms. Lain participated in several research projects pertain- ing to disturbance ecology. Her most recent project focuses on the impacts of hurricane disturbance on migratory songbirds during their spring migration. She also supervised a long-term avian migration research station and database. Over the past several years, Ms. Lain worked as a biology laboratory instructor for biological sci- ences majors and nursing students. Currently she is researching hurricane impacts, teaching biology labs, and working as an instructor for this course.

About the Reviewer

Ms. Scrobola went to King’s College for her pre-med undergraduate degree before going to the University of Scranton for her Master’s in Secondary Education concentrating in biology. She has her Pennsylvania teaching certificate in biology. She taught high school science for a year at Crestwood High School before coming to Penn Foster, starting in admissions and then moving through Student CARE and high school as an academic advisor to finally becoming the college biology and earth science instructor. She also currently teaches biology at Lackawanna County Community College part time.

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07/27/17

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INSTRUCTIONS TO STUDENTS 1

LESSON ASSIGNMENTS 7

LESSON 1: THE CELL 11

LESSON 2: GENETICS 45

LESSON 3: EVOLUTION AND THE DIVERSITY OF LIFE 73

LESSON 3 ESSAY QUESTIONS 109

LESSON 4: STRUCTURE AND FUNCTION IN PLANTS AND ANIMALS 111

LESSON 5: ECOLOGY 165

LESSON 5 ESSAY QUESTIONS 183

RESEARCH PROJECT 185

SELF-CHECK ANSWERS 189

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INTRODUCTION Welcome to the wonderful world of biology! Few subjects can teach as much about the world around you as biology. During this course, you’ll gain insight into the origin of life, the rela- tionships among all living organisms and the environment, and even how your own body works.

The course consists of five lessons. Each lesson covers infor- mation from several chapters of the textbook. This study guide gives you your reading assignments for each chapter of your textbook. It also highlights and clarifies important information in each chapter.

At the end of each lesson, you’ll complete an examination covering information from all of the chapters that comprise that lesson.

OBJECTIVES When you complete this course, you’ll be able to

n Describe the characteristics of living things

n Explain and apply the scientific method

n Identify the structure and function of eukaryotic and prokaryotic cells

n Explain the process of photosynthesis

n Identify basic chemistry and the properties of water

n Describe the basic traits of organic molecules

n Describe the steps involved in cellular respiration

n Explain the processes of mitosis and meiosis and identify the phases of each

n Discuss the basic principles of both Mendelian and modern genetics

n Describe the structure and function of DNA and RNA

n Describe the traits of cancer and explain how it develops

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n List the domains and kingdoms of living organisms

n Discuss Darwin’s theory of natural selection and evolution

n Compare and contrast the types of natural selection and evolution

n Compare and contrast the traits of microorganisms

n Differentiate between major plant groups and outline their characteristics

n Identify and describe basic plant anatomy, responses, and reproduction

n List the characteristics of the major classes of invertebrates

n Name and describe seven classes of nonextinct vertebrates

n Discuss the functions of four types of animal tissues

n Identify the components and functions of major human organ systems

n Identify and explain the components of the immune system

n Explain the factors that influence population growth

n Describe the organization and development of communi- ties, as well as the characteristics of ecosystems

n Explain the effects modern human society has had on many of the world’s ecosystems

YOUR TEXTBOOK Your textbook, Essentials of Biology, contains most of the detailed information upon which your examinations are based. Your textbook material is divided into chapters. The pages for each chapter are clearly indicated in the contents.

Instructions to Students2

Listed below are some of the features of your textbook:

n “Learning Outcomes” listed at the beginning of each chapter, to help you focus on what you should learn in the reading

n Short questions at the end of each chapter that test your knowledge about what you’ve read

n Exercises at the end of each chapter that teach you to think critically

n A glossary of key terms

n An index for fast, easy reference of topics

At the end of every chapter in your textbook is a summary. Read this material carefully to check your understanding. Following the summary are a number of tools you can use to review the material you’ve just studied. We highly recommend that you complete “Key Terms,” “Testing Yourself,” “Thinking Scientifically,” and “Bioethical Issue.” The answers to most of these questions and problems are included in Appendix A.

COURSE MATERIALS This course includes the following materials:

1. This study guide, which contains an introduction to your course, plus

n A lesson assignments page with a schedule of study assignments

n Assignment lessons emphasizing the main points in the textbook

n Self-checks and answers to help you assess your understanding of the material

n A research project

2. Your course textbook, Essentials of Biology, which contains the assigned reading material. The McGraw Hill online resource is not part of the course. It is not required.

Instructions to Students 3

Instructions to Students4

Please take a look at the research project at the end of this study guide so you’ll know what’s expected of you in complet- ing the project. You can work on the project as you work through the course. Don’t wait until you complete all the coursework before you begin the research project.

A STUDY PLAN This study guide is intended to help you achieve the maxi- mum benefit from the time you spend on this course. It doesn’t replace the textbook in any way. It serves as an intro- duction to the material that you’ll read in the book and as an aid to assist you in understanding this material.

This study guide divides your course into five lessons. Each lesson contains several assignments, with a self-check for each assignment. A comprehensive examination covers the material from each of the five lessons. Be sure to complete all work related to a lesson before moving on to the next lesson.

Below is a suggested format for using this study guide. Remember that this is just a suggested plan. If you feel that another method would help you learn more effectively, by all means use that method.

1. Note the pages for each assignment.

2. Scan the assigned pages in the textbook. Make a note of the headings and illustrations. Write down questions to yourself.

3. Keep your textbook open to the chapter and read the assignment text in this study guide. When the study guide makes references to passages or figures in the textbook, refer to the text to complete your understand- ing. It may answer your questions or inspire more.

4. Read the assigned pages in the textbook. This time, pay close attention to details. Concentrate on gaining an understanding of the concepts being presented.

5. Check on anything that’s still not clear, and reexamine the pages and illustrations to which the study guide refers. Then complete the self-check. You can check your answers using the answers at the back of this study

guide. If you have problems completing any self-check question, reread the sections of the textbook that pertain to the problem area.

6. Complete each assignment in this way. If you miss any questions, review the pages of the textbook covering those questions. The self-checks are designed to reveal weak points that you need to review. Don’t send the self- check answers to the school. They’re for you to evaluate your understanding of the material.

7. When you’ve completed all of the assignments for the first lesson and you feel confident that you understand the material covered, take the lesson examination.

8. When you receive the results of your examination, don’t dwell on any mistakes you made. Simply note which questions you answered wrong, go back to the textbook to locate the right answer, and move on. A successful learner isn’t someone who never makes mistakes; a suc- cessful learner is someone who learns to benefit from correcting mistakes. After all, once you’ve corrected a mistake, you know the right answer and shouldn’t make the same mistake again.

Repeat these steps for each lesson in this course. At any time, you can contact your instructor for information regard- ing the materials.

You’re now ready to begin Lesson 1. Good luck and have fun!

Instructions to Students 5

Remember to regularly check your student homepage. Your instructor

may post additional resources that you can access to enhance your

learning experience.

NOTES

Instructions to Students6

Lesson 1: The Cell For: Read in the Read in the

study guide: textbook:

Assignment 1 Pages 12–17 Chapter 1

Assignment 2 Pages 18–22 Chapter 2

Assignment 3 Pages 23–27 Chapter 3

Assignment 4 Pages 28–31 Chapter 4

Assignment 5 Pages 32–35 Chapter 5

Assignment 6 Pages 36–39 Chapter 6

Assignment 7 Pages 40–43 Chapter 7

Examination 250100 Material in Lesson 1

Lesson 2: Genetics For: Read in the Read in the

study guide: textbook:

Assignment 8 Pages 46–49 Chapter 8

Assignment 9 Pages 50–53 Chapter 9

Assignment 10 Pages 54–59 Chapter 10

Assignment 11 Pages 60–64 Chapter 11

Assignment 12 Pages 65–67 Chapter 12

Assignment 13 Pages 68–71 Chapter 13

Examination 250101 Material in Lesson 2

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Lesson 3: Evolution and the Diversity of Life For: Read in the Read in the

study guide: textbook:

Assignment 14 Pages 74–78 Chapter 14

Assignment 15 Pages 79–82 Chapter 15

Assignment 16 Pages 83–87 Chapter 16

Assignment 17 Pages 88–93 Chapter 17

Assignment 18 Pages 94–97 Chapter 18

Assignment 19 Pages 99–106 Chapter 19

Examination 250103 Material in Lesson 3 Lesson 3 Essay Examination 25010400

Lesson 4: Structure and Function in Plants and Animals For: Read in the Read in the

study guide: textbook:

Assignment 20 Pages 112–116 Chapter 20

Assignment 21 Pages 117–121 Chapter 21

Assignment 22 Pages 122–126 Chapter 22

Assignment 23 Pages 127–130 Chapter 23

Assignment 24 Pages 131–137 Chapter 24

Assignment 25 Pages 138–141 Chapter 25

Assignment 26 Pages 142–146 Chapter 26

Assignment 27 Pages 147–152 Chapter 27

Assignment 28 Pages 153–158 Chapter 28

Assignment 29 Pages 159–163 Chapter 29

Examination 250106 Material in Lesson 4

Lesson Assignments8

Lesson 5: Ecology For: Read in the Read in the

study guide: textbook:

Assignment 30 Pages 166–170 Chapter 30

Assignment 31 Pages 171–177 Chapter 31

Assignment 32 Pages 178–181 Chapter 32

Examination 250108 Material in Lesson 5 Lesson 5 Essay Examination 25010900

Research Project 25011100

Lesson Assignments 9

Note: To access and complete any of the examinations for this study

guide, click on the appropriate Take Exam icon on your student portal.

You should not have to enter the examination numbers. These numbers

are for reference only if you have reason to contact Student CARE.

NOTES

Lesson Assignments10

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The Cell

INTRODUCTION Your first lesson consists of seven assignments that cover Chapters 1–7 of your textbook. Chapter 1 introduces the science of biology, and Chapters 2–7 cover the cell.

OBJECTIVES When you complete this lesson, you’ll be able to

n Describe the characteristics of living things

n Differentiate between the levels of biological organization

n Describe how organisms are classified

n Discuss the scientific method and its importance in the biological sciences

n Explain the atomic structure of matter and the different kinds of chemical bonds

n Describe the properties of water and explain why it’s vital to life on Earth

n Summarize the properties and different groups of organic molecules

n Describe and explain the structural organization of cells

n Explain the basic processes of diffusion and osmosis

n Describe a basic enzymatic reaction

n Identify the basic processes of photosynthesis

n Discuss the nature of cellular respiration

Introduction to Biology12

ASSIGNMENT 1: A VIEW OF LIFE Refer to the following information as you read Chapter 1 in your textbook.

The Characteristics of Life Biology is the scientific study of life. Several characteristics help to define the term life:

1. All living things (organisms) are composed of cells that contain genes. Genes are composed of DNA inherited from a parent through reproduction.

2. All living things obtain energy from their surroundings and use it to grow, develop, and maintain specific inter- nal conditions.

3. Living organisms can sense changes in their environment and adjust their activities in response to those changes.

4. Living organisms exhibit modifications that represent adaptations to their environment.

Chapter 1 begins with a discussion on the abundance of bacterial flora found on the surface of the human body. Diverse life exists nearly everywhere on Earth. Scientists have barely begun to estimate the number of species living on the planet. Despite the tremendous variation that exists among species, all living things share certain characteristics. Review Figure 1.2 on page 3 to consider the levels of biological organization from molecules to organ systems. The cell, which you’ll study throughout this lesson, is the smallest unit of biological organization that displays all of the charac- teristics of life. In complex multicellular organisms, cells form specialized tissues, organs, and organ systems. Then this organization continues all the way up to the biosphere.

Evolution: The Core Concept of Biology Just as all living organisms share many of the same charac- teristics, overwhelming evidence suggests that they also originated from a common, ancient ancestor. Evolution is the process by which species arise and change over time through

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the process of natural selection. Examine Figure 1.6 on page 7 of your textbook to view an evolutionary tree with the line- ages of major life forms and an overview of how life developed on Earth over the past 3.5 billion years.

Natural Selection

Natural selection is the process whereby a population devel- ops adaptations to its environment, and is what leads to evolution over a long period of time. Four conditions must be met for natural selection to occur:

1. Population members exhibit differences that are heritable (can be inherited).

2. Population members produce more offspring than can be supported by the environmental resources.

3. Competition exists between population members for limited resources and results in increased survival and reproduction of better adapted individuals.

4. Through many generations, a greater portion of the pop- ulation exhibits adaptations to the environment and thus the population as a whole evolves.

Pages 7–8 of your textbook provide some interesting examples that will help you understand how evolution, or descent with modification, occurs over time.

Organizing the Diversity of Life

Biologists use the science of taxonomy to classify organisms into groups according to the ways in which they’re related to one another. Classification categories range from the most specific (a species) to the very general (a domain). Each species has a binomial (two-part) scientific name that consists of both the genus and species names.

Introduction to Biology14

The standard system of classification separates all living organisms into three domains (Archaea, Bacteria, and Eukarya). Following is an explanation of each:

1. Domain Archaea is made up of prokaryotic, unicellular organisms that live in extreme habitats, such as deep ocean steam vents. Prokaryotic organisms lack the membrane-bounded nucleus and membranous organelles typical of eukaryotes.

2. Domain Bacteria consists of prokaryotic, unicellular bac- teria. They inhabit a wide variety of environments and display a remarkable range of adaptations.

3. Domain Eukarya consists of four kingdoms:

a. Kingdom Protista are organisms that may be unicellu- lar, multicellular, or colonial. They have more internal complexity than prokaryotes.

b. Kingdom Fungi are eukaryotic, multicelled organisms that display extracellular digestion. That is, they break down dead organic debris as a source of sustenance.

c. Kingdom Plantae are multicelled, eukaryotic organisms with vascular tissues that use photosynthesis to pro- duce energy. Photosynthesis is the process of using sunlight to synthesize sugars from raw materials.

d. Kingdom Animalia are eukaryotic, multicelled, con- sumers (that is, they don’t produce their own nutrients) that are usually mobile.

Review the photographs and accompanying text in Table 1.2 on page 10 for an overview of the biological domains and kingdoms.

Science: A Way of Knowing Biology has countless fields of emphasis ranging from ecology to biochemistry. Scientists use the scientific method to guide their research and gain a better understanding of natural phenomena.

The scientific method involves the following steps:

1. Develop a question that you would like to answer based on observations you’ve made.

Lesson 1 15

2. Based on your observations and on the findings of past scientists, develop a hypothesis, your best possible expla- nation to the question posed.

3. Based on your hypothesis, make predictions on what you think will occur.

4. Find ways to test your predictions by conducting experi- ments or by making further observations.

5. Develop conclusions by analyzing and reporting your test results.

To test a hypothesis, scientists will often conduct an experi- ment, which is a series of steps designed to test an idea. Experimental design is important in identifying which vari- ables are to be involved and tested within an experiment. When a scientific study is carried out in a laboratory setting, environmental conditions can be more closely controlled while the experimental variable is changed or manipulated. Test groups are provided with the experimental variable while control groups are not.

A common example is the testing of a new drug—the test group receives the drug while the control group unknowingly receives a placebo, a harmless substitute. Data collected dur- ing the experiment are analyzed and then followed by a conclusion to accept or reject the hypothesis. If there isn’t sufficient evidence to provide support for the hypothesis, the experimental results can often help a scientist formulate a new hypothesis to test and the process continues. Figure 1.8 on page 11 presents a flow diagram describing the various steps of the scientific method. Study this figure and then view Figure 1.10, an example of a controlled study on pages 14–15. An experiment must be repeatable—that is, another scientist should be able to repeat the same study carried out previ- ously and achieve the same results.

The scientific community typically communicates their research findings and experimental methods with each other via publication in scientific journals. Articles are peer- reviewed, meaning that they’re reviewed for quality by other experts in the same discipline and that only accepted work gets published. This process helps to ensure the quality and

Introduction to Biology16

accuracy of published scientific information. Sharing research results is a vital part of the scientific process, and is necessary for scientists to be able to expand upon previous findings.

A scientific theory, or widely accepted explanation for a natural phenomenon, is formed when the research of many scientists provides support for the theory. When a theory is supported by the findings of multiple studies over a long time period and becomes widely accepted by the scientific commu- nity, a theory is sometimes then referred to as a principle, or law. Examples include the law of gravity and the principle of evolution.

Challenges Facing Science Technologies developed from the biological sciences often provide mixed blessings. For example, the use of fertilizers helps increase agricultural efficiency and productivity. On the other hand, fertilizer runoff from farmlands can contaminate groundwater and cause other kinds of ecological damage. Since science is impartial and involves no moral judgment, humans as a society are responsible for making decisions on which technologies should be used as well as their best methods for use. Bioethics pertains to the development, implementation, and consequences of biological technologies.

Lesson 1 17

Self-Check 1 At the end of each section of Introduction to Biology, you’ll be asked to pause and check

your understanding of what you’ve just read by completing a “Self-Check” exercise.

Answering these questions will help you review what you’ve studied so far. Please com-

plete Self-Check 1 now.

1. _______ are the smallest units of life.

a. Protons c. Molecules

b. Cells d. Proteins

2. Which one of the following lists shows the correct order of biological organization?

a. Ecosystem, population, community, biosphere

b. Community, population, biosphere, ecosystem

c. Population, community, ecosystem, biosphere

d. Biosphere, community, population, ecosystem

3. A modification that makes organisms more suited to their environment is called a/an

a. selection. c. adaptation.

b. evolution. d. variation.

4. The life domain whose members live in very harsh environments, such as salt lakes and hot

springs, is

a. Fungi. c. Archaea.

b. Bacteria. d. Eukarya.

5. During a scientific experiment, the control group is

a. identical to the experimental group.

b. not aware of the experiment taking place.

c. different from the experimental group in all respects.

d. identical to the experimental group in all areas except the variable being tested.

Check your answers with those on page 191.

Introduction to Biology18

ASSIGNMENT 2: THE CHEMICAL BASIS OF LIFE Refer to the following information as you read Chapter 2 in your textbook.

Atoms and Atomic Bonds Everything on Earth, whether it’s a liquid, a solid, or a gas, is considered matter. All matter is composed of elements, which are substances that can’t be broken down into any other substance. The atomic theory states that elements are com- posed of small particles named atoms.

Atomic Structure

The nucleus, or center, of an atom is composed of protons (positively charged particles) and neutrons (uncharged parti- cles). Under most conditions, electrons (very light negatively charged particles) balance the positive charges of nuclear protons.

The number of protons in the nucleus of an atom gives it a unique atomic number. For example, oxygen contains eight protons in its nucleus and has an atomic number of eight. Hydrogen contains one nuclear proton and has an atomic number of one. On page 23 of your textbook, the diagram in Figure 2.2 illustrates the protons, neutrons, and electrons in an atom of helium.

The Periodic Table

The periodic table is a tabular arrangement of the chemical elements according to atomic number. As shown on page 23, the number that appears above the atomic symbol represents the atomic number, or the number of protons in the nucleus of the element. Figure 2.3 illustrates a portion of the periodic table of the elements.

Lesson 1 19

Atoms of a particular element can vary in the number of neutrons they contain. Atoms that vary in neutron number are called isotopes. Some unstable isotopes—like carbon-14— are radioactive. Your textbook provides some examples of the uses of radioactive isotopes in a medical setting on page 24.

Arrangement of Electrons in an Atom

Electrons orbit around atomic nuclei in energy shells that represent particular energy levels. The shell nearest the nucleus can hold a maximum of two electrons, while each additional shell may hold up to eight electrons. An atom with one electron shell is complete, and most stable, with two elec- trons. The octet rule states that an atom with two or more electron shells is most stable when the outer shell, or valence shell, contains eight electrons. Figure 2.6 on page 25 of your textbook illustrates the atoms of the six elements most important to life—“CHNOPS,” or carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. You should be able to recog- nize and draw the shell models for these elements.

Types of Chemical Bonds

Based on how their electrons interact, two or more atoms can join to form a molecule. If a molecule is composed of atoms of different elements, it’s called a compound. For this course, you should understand the following two types of atomic bonding:

1. Ionic bonding occurs when atoms either donate or accept electrons from another atom. For example, ionic bonding may occur when one atom has a vacancy in its outer shell and another has one electron in its outer orbital that can be easily removed. The atom that donates an electron becomes positively charged, and the atom that gains an electron becomes negatively charged. The two atoms are now attracted to each other and can join to form a molecule. Review Figure 2.7 on page 26 to visual- ize the way chlorine and sodium join to form molecules of sodium chloride—common table salt.

Introduction to Biology20

2. Covalent bonding occurs when each of two atoms has an unpaired electron in its outer electron shell. Each atom exerts a force on the unpaired electron of the other, pulling them together. The unpaired electrons are then shared between the two atoms. This sharing of electrons may be equal between the two atoms, producing what’s called a nonpolar bond. It may also be unequal, causing one end of the molecule to have a slight positive charge and the other end to have a slight negative charge. Unequal electron sharing produces a polar covalent bond. Covalent bonding is illustrated in your textbook on page 27.

Water’s Importance to Life Water is the most important substance on Earth because life can’t occur without it. Review the structure of water on page 29 of your textbook. The water molecule has several unique, life-sustaining properties:

1. Water is a solvent. Water molecules attract other polar molecules and can even cause them to separate. In a water solution, for example, sodium chloride is dissoci- ated into negative (Cl–) and positive (Na+) ions.

2. Water is cohesive and adhesive. The cohesive quality of water causes its molecules to cling to each other; the adhesive quality of water causes water to stick to polar surfaces. Both of these qualities make water an excellent transport system. See Figure 2.10 on page 30 of your text, which describes how these cohesion and adhesion qualities allow for the movement of water through a tree.

3. Water has a high surface tension. Because of the strong hydrogen bonding in water, it has a high surface tension. That is, the molecules on the surface of the liquid are attracted to each other, thereby creating a barrier between the air and the liquid. This property is what allows us to “skip rocks,” and what allows insects and other small animals to move across the surface of water.

Lesson 1 21

4. Water has a high heat capacity. Because of this quality, water helps to stabilize temperature by absorbing large amounts of heat energy. Additionally, water requires very high temperatures before it will change into a gaseous form.

5. Water is less dense in its solid state. As water freezes, it becomes less dense. Therefore, ice floats and forms on top of bodies of water. Without this property, bodies of water might freeze completely and prevent life from exist- ing in the water during winter.

Acids and Bases If water molecules dissociate, they yield an equal quantity of hydrogen ions (H+) and hydroxide ions (OH–). Therefore, water is neither acidic nor basic. On the other hand, if vinegar is added to a water solution, the result is a higher concentration of H+. An acid is a substance that dissociates when added to water and releases H+. Therefore, a vinegar solution, or any solution with a high concentration of H+, is acidic. By contrast, if ammonia is added to a water solution, hydroxide ions (OH–) are released and the solution becomes more basic. A base is a substance that either releases OH– or takes in H+. The pH scale is used to indicate the concentration of H+ in a solution. Drastic changes in pH can negatively impact living organisms in various ways. Review the information about acids, bases, and pH level, and their importance, on pages 33–35.

Introduction to Biology22

Self-Check 2 1. The _______ is a subatomic particle that carries a positive electrical charge.

a. electron c. isotope

b. proton d. neutron

2. When an atom has two or more electron shells, the outer shell will be most stable if it con-

tains eight electrons. This concept is called the

a. valence rule. c. octet rule.

b. rule of eight. d. isotope rule.

3. When two oxygen atoms join together, a _______ is formed.

a. mixture c. compound

b. shell model d. molecule

4. The _______ bond is a type of atomic bond in which atoms share electrons to produce a com-

pleted outer shell.

a. ionic c. colloquial

b. covalent d. isotonic

5. The polarity of water molecules causes them to be attracted to one another by a _______

bond.

a. covalent c. hydrogen

b. polarized d. hydrophilic

6. As the number of hydrogen ions in a solution increases, the pH of the solution

a. decreases. c. increases.

b. stabilizes. d. neutralizes.

7. During winter only the upper surface of a lake freezes, which allows for life to persist below

the surface. Which of water’s unique properties is responsible for this phenomenon?

a. High heat capacity c. Adhesiveness

b. High surface tension d. Lower density as ice

8. The most abundant element by weight in the human body is

a. nitrogen. c. sulfur

b. carbon. d. oxygen.

Check your answers with those on page 191.

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ASSIGNMENT 3: THE ORGANIC MOLECULES OF LIFE Refer to the following information as you read Chapter 3 in your textbook.

Organic Molecules Organic chemistry is the study of the chemical compounds involving carbon. Since living things are composed mainly of water, water can be considered the medium of life. But the organic compounds that depend on that medium are based on the chemical properties of carbon and hydrogen. Carbon is the key to life on earth because of its unique bonding prop- erties. With four electrons in its outer shell, carbon readily adds four additional electrons to complete its outer shell. Carbon-hydrogen compounds range from simple methane (CH4) to incredibly complex compounds comprised of long chains or rings of carbon atoms. Review Figure 3.2 on page 40 to consider the versatility of hydrocarbons (molecules that are chains of carbon atoms bonded to hydrogen atoms).

Organic chemists identify two basic parts of a hydrocarbon skeleton—a functional group and a wide range of carbon- based molecular arrangements that can be simply denoted as R. The carbon backbone provides structural support while the functional group determines the reactivity of an organic molecule. Study Figure 3.3 and read the accompanying text on page 40 to learn about the function, structure, and impor- tance of functional groups.

The Biological Molecules of Cells Carbohydrates, lipids, proteins, and nucleic acids are the four groups of organic molecules, known as biological molecules, and are based on carbon atoms. As the basic organic com- pounds of life, each carbon atom can share electrons with up to four other atoms, forming stable covalent bonds. Carbon atoms tend to link together into chains, forming a functional

Introduction to Biology24

group backbone to which R elements can become attached. Review Figure 3.7 and adjacent text that introduces organic molecules and describes their basic reactions.

Carbohydrates

Carbohydrates consist of carbon, hydrogen, and oxygen in a 1:2:1 ratio. Cells use them for energy as well as structural materials. There are three main classes of carbohydrates:

1. Monosaccharides are simple sugars that have one sugar molecule. Their carbon backbone is composed of three to seven carbon atoms. Examples are glucose, fructose, and ribose. As you’ve already learned, glucose is the most basic source of energy for living things. On page 42, study Figure 3.8 to review the nature of glucose.

2. Disaccharides are composed of two monosaccharides that are bonded together. Examples of disaccharides include lactose (milk sugar), sucrose (table sugar), and maltose. Figure 3.9 on page 43 illustrates the breakdown of the disaccharide maltose.

3. Polysaccharides are complex carbohydrates with many monosaccharide molecules that form chains or branches. Examples include glycogen, starch, and cellulose. Polysaccharides often carry out short-term energy stor- age; for instance, glycogen stores energy in the livers of animals. Polysaccharides also can serve as structural components of cells. Cellulose, abundant in plants, is the most common structural polysaccharide on our planet. Another polysaccharide, chitin, forms the shells of crabs and lobsters as well as the exoskeletons of insects. Figure 3.10 on page 44 shows the structure and function of starch and cellulose.

Lipids

Lipids are fats and other oily organic substances. Cells use lipids for energy storage, for structural support, and as sig- naling molecules. Lipids are nonpolar hydrocarbons that don’t dissolve in water. Lipids are composed of fatty acids attached to glycerol. Fatty acids may be saturated or unsaturated.

Lesson 1 25

Saturated fatty acids, which are associated with cardio – vascular disease, should be avoided in foods. By contrast, unsaturated fats protect against fat buildup in arteries.

Triglycerides are the most abundant lipids in the body. When broken down, they provide more than twice the energy of complex carbohydrates. Study Figure 3.12 on page 46 to visualize saturated and unsaturated fatty acids. Note the car- boxyl functional group.

Phospholipids are structurally important lipids found in the plasma membranes that surround cells. Among these lipids are steroids, which serve regulating functions in humans. Cholesterol is a steroid in the plasma membranes of animals. It’s also a precursor of the male sex hormone testosterone and the female sex hormone estrogen. Study Figure 3.14 on page 47 to view the fused hydrocarbon rings of steroids.

Proteins

Proteins are the vital infrastructure of life.

n Keratin (which makes up hair and fingernails) and collagen (which supports skin and tendons) provide structural support.

n Enzymes act as catalysts, which speed the basic chemi- cal reactions of life and sustain the life-energy economy called metabolism.

n Hemoglobin in red blood cells transports oxygen to cells throughout the body.

n Antibodies help protect us from disease.

n Hormones coordinate chemical communications among cells and regulate levels of vital nutrients like glucose.

n Actin and myosin are proteins that allow animals to walk, run, and fly. Working together, these proteins per- mit muscle cells to contract and relax in the rhythms of motion.

Introduction to Biology26

Proteins are composed of chains of amino acids joined by peptide bonds. A peptide bond is formed when an amino group bonds covalently to a carboxyl group. Study Figure 3.16 to learn the basic structure of the 20 kinds of amino acids and Figure 3.17, illustrating the hydrolysis and dehydration reactions that characterize peptide bonds.

A peptide is made of two or more amino acids joined together by covalent bonds. A polypeptide is a molecule that consists of many amino acids connected by peptide bonds.

The sequence of amino acids in each type of protein is highly specific, giving a protein its primary structure. While all pro- teins have a primary structure, different kinds of proteins take on characteristic shapes. Fibrous proteins, like keratin and collagen, perform their support roles precisely because they have a distinctive, secondary helical structure. Globular proteins have a tertiary structure that has a three-dimensional shape. Very complex proteins, like hemoglobin for example, have more than one polypeptide bond. Therefore, they have a quaternary structure. This structure is best understood if visualized, so carefully study Figure 3.18 on page 50. If a protein becomes denatured, it means it has lost its character- istic shape and function.

Nucleic Acids

Small organic compounds that contain one or more phosphate groups and a five-carbon sugar attached to a nitrogenous base are called nucleotides. Nucleic acids are polymers of nucleotides that occur as single (as in RNA) or double (as in DNA) strands of covalently bonded nucleotides that store genetic information, or genes that code for specific proteins. Adenine, guanine, cytosine, and thymine are the bases that occur in DNA. RNA is composed of the bases adenine, gua- nine, cytosine, and uracil. Study Figure 3.19 on page 51 of your textbook to review the structure of nucleotides in gen- eral and DNA and RNA specifically. Adenosine triphosphate (ATP) is an important nucleotide that works as an energy car- rier within cells.

Since DNA contains genes that code for the sequence of amino acids for a specific protein, even a small flaw in the genetic code can cause illness. View the example provided in Figure 3.20 on page 52 of your textbook for sickle cell disease.

Lesson 1 27

Self-Check 3 1. The polysaccharide structural carbohydrate most commonly used by living things is

a. starch. c. keratin.

b. glycogen. d. cellulose.

2. Which one of the following functional groups is associated with fatty acids?

a. Phosphate c. Carboxyl

b. Amino d. Hydroxyl

3. The hard body parts of insects and crabs are composed of a polysaccharide called

a. cellulose. c. glycogen.

b. chitin. d. glucose.

4. Cell membranes are composed mainly of which type of lipids?

a. Phospholipids c. Steroids

b. Waxes d. Glycerides

5. _______ proteins are made of polypeptide chains folded into rounded compact shapes.

a. Fibrous c. Helical

b. Pleated d. Globular

6. When joined by a dehydration reaction, the covalent bond between the carboxyl groups of two

amino acids is called a _______ bond.

a. peptide c. hydrogen

b. carboxyl d. hydroxyl

7. The sugar in RNA is

a. deoxyribose. c. glucose.

b. ribose. d. sucrose.

Check your answers with those on page 191.

Introduction to Biology28

ASSIGNMENT 4: INSIDE THE CELL Refer to the following information as you read Chapter 4 in your textbook.

Cells under the Microscope With very few exceptions, cells are too small to be seen with- out a microscope. Cells are small so as to maximize the surface-area-to-volume ratio and increase the surface area for exchange of nutrients and wastes. A small cell has a greater surface-area-to-volume ratio than a larger cell. Review this topic on page 58 to make sure you understand this principle. Because of this greater ratio, smaller cells are better adapted to exchanging gases and nutrients with their fluid environ- ments. Carefully study Figure 4.2, which illustrates the relative sizes of living things and their components.

The Plasma Membrane The boundary between the inside and the outside of any cell is the plasma membrane. In all cells, this cell boundary is composed of a lipid bilayer whose hydrophobic (water-repellent) tails are sandwiched between the hydrophilic (water-loving) heads. Proteins embedded within or attached to the lipid bilayer allow the movement of water-soluble substances into and out of the cell. Figure 4.4 on page 60 illustrates the gen- eral features of a plasma membrane.

The functions of the plasma membrane proteins include channeling, transporting, cell recognition, receptor functions, enzymatic processes, and forming junctions for cell-to-cell communication. These functions are explained on page 61. Study Figure 4.5 on page 61 to master your understanding of the membrane proteins.

Lesson 1 29

The Two Main Types of Cells The cell is the smallest unit that has the potential to live on its own. All cells have a plasma membrane that encloses their cytoplasm and genetic material. There are two fundamentally different types of cells. Eukaryotic cells have a nucleus as well as other membrane-bound organelles. Prokaryotic cells, represented in your text by bacteria, lack a membrane- bounded nucleus. Instead, their genetic material is located in a nucleoid. Study Figure 4.6 on page 63, which describes the structures and functions of a prokaryotic cell.

Eukaryotic Cells The vast majority of cells in nature are eukaryotic; therefore, you should make sure you’re quite clear on the structures and functions of this type of cell. You should be able to label drawings of plant and animal cells after studying Figure 4.7 on page 64 (for animal cells) and Figure 4.8 on page 65 (for plant cells).

The nuclear envelope, a double membrane surrounding the nucleus of eukaryotic cells, protects the DNA within it. The nucleus separates the DNA molecules from the cytoplasm, thus making it easier for the cell to replicate its DNA before cell division occurs. The presence of a double nuclear membrane also allows for strict control of the passage of substances to and from the cytoplasm. See pages 66–67 to review the structure and function of the nucleus.

The endoplasmic reticulum (ER) is continuous with the nuclear envelope and extends into the cytoplasm. An ER with ribosomes attached is called a rough ER, whereas an ER without ribosomes is called a smooth ER. Ribosomes are responsible for synthesizing polypeptide chains. Smooth ER curves through the cytoplasm and functions in lipid synthe- sis. Vesicles are small, membranous sacs that transport molecules. Figure 4.12 on page 69 illustrates the organelles of the endomembrane system. Vacuoles are similar to vesicles except they’re larger and are usually used to store substances.

Introduction to Biology30

Golgi apparatus bodies modify polypeptide chains into mature proteins before shipping them out to specific locations within the cell. They’re composed of flattened, membrane-bound sacs that resemble a stack of pancakes.

The mitochondria (Figure 4.15) are often called the “power- houses” of a cell. Adenosine triphosphate (ATP), which the body uses for energy, is formed from the breakdown of organic compounds within a mitochondrion. Each mitochon- drion has a double membrane system. The inner membrane is folded to create compartments within the organelle itself.

Chloroplasts are specialized organelles present in photo – synthetic plant cells. The first stage of photosynthesis begins in a special area of the chloroplast called the thylakoid membrane, where energy from sunlight is used to form ATP molecules. Review and study Figure 4.14 on page 70 to visu- alize chloroplast structures.

The cytoskeleton of a eukaryotic cell extends from the nucleus to the plasma membrane. Comprising different kinds of protein filaments and microtubules, it serves as a sort of framework or internal scaffolding for the cell. Study Figure 4.17 on page 72 to learn the nature and functions of microtubules.

Outside the Eukaryotic Cell All plant cells have cell walls that are connected by plasmodesmata, which contain numerous tiny channels that allow direct exchange among grouped cells. Animal cells, on the other hand, don’t have cell walls. Instead, they have an extracellular matrix of polysaccharides and proteins. Remember that many cell types are grouped as tissues by three different types of junctions.

n Adhesion (stretchy) junctions form between the cells of heart and bladder tissues.

n Tight junctions make for tight cell connections as cell wall proteins actually attach to each other.

n Gap junctions—as in muscle tissues—consist of channels that allow direct communication by way of flowing ions.

Lesson 1 31

Self-Check 4 1. Within cells, the synthesis of proteins occurs in the

a. nuclear envelope. c. chromatin.

b. ribosomes. d. nucleolus.

2. What is the main function of the mitochondria?

a. Assembling polypeptide chains c. Producing ATP

b. Digesting substances d. Moving internal structures

3. The _______ keep(s) the cytoplasm of eukaryotic cells separate from the DNA.

a. Golgi body c. chromosomes

b. ribosomes d. nuclear envelope

4. Organelles that use solar energy to make carbohydrates are called

a. chloroplasts. c. centrioles.

b. mitochondria. d. lysosomes.

5. The _______ are sometimes called the “powerhouses” of the cell.

a. ER c. chloroplasts

b. mitochondria d. nuclei

6. The cell-to-cell junctions that allow cells to communicate are called _______ junctions.

a. gap c. matrix

b. adhesion d. tight

Check your answers with those on page 192.

Introduction to Biology32

ASSIGNMENT 5: THE DYNAMIC CELL Refer to the following information as you read Chapter 5 in your textbook.

What Is Energy? All organisms must secure energy from their environment to be used for metabolic processes. Energy occurs in two main forms: potential and kinetic energy, as described on page 80.

The first law of thermodynamics states that energy can’t be created or destroyed, but is transformed from one form to another. For example, when a plant absorbs energy from the sun and converts it into chemical energy, the cells of an organism that eats the plant may convert that energy into mechanical energy for movement, or perhaps use it for chem- ical energy to build or break apart substances within its cells. But every time this energy is converted to another form, some is lost to the environment as heat. The energy that’s lost can’t be recaptured, which illustrates the second law of thermodynamics. The second law states that energy can’t be transformed from one form to a different one without a loss of some usable energy. In other words, every change in form is accompanied by increasing levels of disorganization, or entropy.

ATP: Energy for Cells ATP is the main molecule of stored energy used by cells. ATP is a nucleotide, the kind of molecule that serves as a monomer in DNA and RNA. ATP contains the sugar ribose, a nitrogen-containing base adenine, and three phosphate groups. See Figure 5.3 on page 82.

Figure 5.4 on page 83 illustrates the ATP cycle. The cycle is driven by coupled reactions that occur in the process of cellular respiration. Coupled reactions take place when an energy-releasing reaction occurs along with an energy- requiring reaction. See Figure 5.5 on page 84 and note how coupled reactions occur during muscle contraction. The

Lesson 1 33

world of living things is sustained in renewable cycles— illustrated by the ATP cycle. Review and study Figure 5.6 on page 85, and think about the energy flow from plants to ani- mals and back again.

Metabolic Pathways and Enzymes A metabolic pathway is a chain or series of linked reactions— like those related to the ATP cycle. They start with a particular chemical reaction and end with a product of a chain of reac- tions. In an enzymatic reaction, the reactants are called substrates. Metabolic reactions inside cells wouldn’t occur fast enough to keep an organism alive without enzymes.

Enzymes are proteins that speed up the rate of a metabolic reaction. They don’t cause reactions to occur—they just make them occur many times faster than they would otherwise. Enzymes aren’t used up once they jump-start a reaction; rather, they may be used over and over again. Each type of enzyme recognizes certain substrates and binds to them in specific ways. As soon as the enzyme binds to an active site on a substrate, it catalyzes, or sets into motion, a reaction. Cells have control mechanisms to adjust how quickly enzymes are produced and to stop an enzyme’s action when reactions are no longer necessary. Figure 5.7 on page 86 helps you visualize the way an enzyme does its job. Figure 5.9 on page 87 helps you visualize how, through feedback, the products of a reaction can serve to regulate a metabolic pathway— stopping it when enough is enough.

Figure 5.9 on page 87 illustrates the idea of energy of activation, which is the amount of energy needed to begin a chemical reaction. The figure shows how catalytic enzymes add to the energy available for a series of reactions.

Cell Transport Substances like nutrients, enzymes, and so on must get into cells if the cells are to function properly. These substances enter cells in one of three ways:

1. Passive transport requires no energy on the part of the cell. The energy of moving molecules in a fluid does the trick. One type of passive transport is simple diffusion.

Introduction to Biology34

To see how this works, lay out a paper towel. Drip some water onto one end of the sheet and notice how the water spreads outward all of its own accord. Another example of simple diffusion is illustrated for you in Figure 5.10 on page 88. Osmosis, another type of passive transport, is illustrated in Figures 5.12 and 5.13. In osmosis, water molecules diffuse across a membrane from an area of greater concentration to an area of lower concentration.

2. Active transport through a cell’s plasma membrane requires energy from the cell. Figure 5.14 on page 90 shows how transport proteins in a plasma membrane use energy to move a solute across the membrane. Proteins that do this kind of work are often called pumps.

3. Bulk transport is illustrated in Figure 5.15 on page 91. In this process, cell membranes form to capture groups of macromolecules for exocytosis (export) or endocytosis (import).

Lesson 1 35

Self-Check 5 1. In a/an _______ reaction, one reaction releases energy and the second uses energy.

a. paired c. coupled

b. energetic d. diverted

2. Which of the following is not a feature of enzymes?

a. They drive reactions in a forward direction.

b. They bind to a substrate during a reaction.

c. Metabolic reactions destroy the enzyme molecules.

d. They speed up reaction time.

3. The term entropy refers to

a. the absorption of heat.

b. the relative amount of disorganization in a system.

c. an open system.

d. the first law of thermodynamics.

4. The term phagocytosis refers to a type of

a. vesicle. c. endocytosis.

b. exocytosis. d. passive transport.

5. _______ is the movement of water across a semipermeable membrane from an area of higher

concentration to an area of lesser concentration.

a. Active transport c. Endocytosis

b. Osmosis d. Diffusion

Check your answers with those on page 192.

Introduction to Biology36

ASSIGNMENT 6: ENERGY FOR LIFE Refer to the following information as you read Chapter 6 in your textbook.

Overview of Photosynthesis Plants, algae, some protists, and all cyanobacteria (bacteria that contain chlorophyll) use carbon dioxide, water, and energy from sunlight to make glucose through the process of photosynthesis. This important process creates most of the carbohydrates and oxygen used by living organisms on Earth. Review Figure 6.1 on page 96, with examples of a variety of photosynthesizing organisms.

In flowering plants, photosynthesis takes place in the chloroplasts of cells. The first stage occurs in the thylakoids (stacked into grana) where light energy is trapped and con- verted to ATP during light-dependent reactions. Chlorophyll and other pigments are found within thylakoid membranes. The stroma, a fluid-filled area inside a chloroplast, is where dark reactions, or second-stage reactions, of photosynthesis occur. The stroma reactions don’t require light, but they do require the energy produced by light during the first-stage reactions. Study Figure 6.2 on page 97 to review the role of plant leaves in photosynthesis. Gas exchange occurs via small pores, or stomata, in the surface of a leaf. There are two kinds of reactions involved with photosynthesis—light reactions and second-stage Calvin cycle reactions.

The Light Reactions—Harvesting Energy Pigment molecules in leaves absorb certain wavelengths of light and reflect the rest. Chlorophylls are the primary pig- ments involved with photosynthesis. They absorb most wavelengths of light and reflect only green, which is why plants appear green to us. Carotenoids, on the other hand, absorb blue-violet and blue-green wavelengths and reflect

Lesson 1 37

red, orange, and yellow. Carotenoid pigments give fall leaves their dramatic color. Figure 6.5 on page 100 summarizes how leaf pigments absorb and reflect different wavelengths.

Flowering plant pigments capture solar energy to split water into hydrogen, oxygen, and electrons. Electron transport systems then move these electrons step by step through a pathway containing enzymes and coenzymes that assist with the reactions. Energy that escapes at each step drives the formation of ATP and NADPH (nicotinamide adenine dinucleotide phosphate).

The light reactions use two photosystems (PS) for electron flow: PS II splits water, and PS I produces NADPH. Thoroughly review pages 100–102 and accompanying Figures 6.6–6.7 to better understand the electron transport chain, thylakoid organization, and the processes that lead to the Calvin cycle reactions.

The Calvin Cycle Reactions—Making Sugars Calvin cycle reactions, carried out in the stroma of chloro- plasts, use carbon dioxide from the atmosphere to produce a carbohydrate. The reactions require energy from the ATP and NADPH formed during the light reactions. The first step of the cycle is carbon dioxide fixation. During this step, CO2 is attached to RuBP, a five-carbon molecule that acts as a sub- strate for the enzyme RuBP carboxylase (rubisco). Rubisco drives a reaction that ends up with three carbon molecules.

The next step, reduction of CO2, uses NADPH and some ATP to produce a carbohydrate, which is usually glyceraldhyde-3- phosphate (G3P). G3P can be broken down to produce glucose. However, G3P is versatile, and plants can use it to produce all the hydrocarbon molecules they need, including glucose, cellulose, and even fatty acids.

The final step in the Calvin cycle is the regeneration of RuBP. This step is necessary before the cycle can be repeated. Note that it takes three “turns” of the Calvin cycle to produce one G3P molecule. Study Figure 6.8 on page 103 to examine the Calvin cycle reactions.

Introduction to Biology38

Other Types of Photosynthesis Just as plants vary in their physical adaptations to the envi- ronment, they also have adapted metabolically. The three types of photosynthesis discussed in your textbook are C3 photosynthesis, C4 photosynthesis, and CAM photosynthesis.

Some plants, including most of the familiar flowering plants, are adapted to areas that have moderate rainfall. These plants are said to utilize a C3 photosynthesis system, because the first detectable molecule after CO2 fixation is a C3 mole- cule. During the Calvin cycle, CO2 fixation occurs within chloroplasts found in mesophyll cells.

C4 photosynthesis occurs in plants that have adapted to arid conditions and/or environments with high levels of light intensity. These plants, called C4 plants, include corn and sugarcane.

CAM photosynthesis occurs in plants adapted to warm, arid environments, such as bromeliads like the pineapple, and cacti and other succulents. The CAM system is unique because it divides different stages of photosynthesis into nighttime and daylight phases. View Figures 6.10, 6.11, and 6.12 on pages 105–106 and compare carbon dioxide fixation in C3, C4, and CAM plants.

Lesson 1 39

Self-Check 6 1. In the electron pathway for light reactions in photosynthesis, PS II involves

a. splitting water. c. producing coenzymes.

b. the production of NADPH. d. the production of ATP.

2. A plant that absorbs blue-violet-green wavelengths of light, will reflect what color?

a. White-yellow c. Yellow-orange

b. Blue d. Green

3. _______ is an example of a CAM plant.

a. Corn c. Sugarcane

b. Pineapple d. Crabgrass

4. The final step of the Calvin cycle is the regeneration of

a. ATP. c. RuBP.

b. electrons. d. G3P.

5. Atmospheric carbon dioxide enters leaves through

a. stroma. c. thylakoids.

b. grana. d. stomata.

Check your answers with those on page 192.

Introduction to Biology40

ASSIGNMENT 7: ENERGY FOR CELLS Refer to the following information as you read Chapter 7 of your textbook.

Cellular Respiration Cellular respiration produces ATP—the energy source neces- sary for organic processes. In cellular respiration, oxidation of substrates is crucial. However, unlike in the case of burn- ing wood, where oxygen is (rapidly) added, oxidation in cellular respiration amounts to removing hydrogen atoms from glucose. Glucose, in turn, is broken down to release energy.

Outside the Mitochondria: Glycolysis The four phases in the complete breakdown of glucose are summarized in Figure 7.2 on page 112.

Glycolysis, the first phase in the breakdown of glucose, takes place in the cytoplasm outside the mitochondria. During gly- colysis, glucose (a 6-carbon molecule), is broken down into two 3-carbon pyruvate molecules. Glycolysis occurs in two steps; during energy-investment steps, two ATP molecules are broken down to release energy used in subsequent reactions, and in energy-harvesting steps oxidation produces substrates with energized phosphate groups. The end result of a chain of reactions is a yield of two pyruvate molecules for each glu- cose molecule. If oxygen is present in the cytoplasm, the pyruvates then enter mitochondria for further processing. To follow the glycolysis reactions, study Figure 7.3 on page 113.

Outside the Mitochondria: Fermentation Fermentation is the anaerobic breakdown of glucose to pro- duce ATP and a toxic end product of some kind. Anaerobic means “in the absence of oxygen.” During this process, one

Lesson 1 41

molecule of glucose yields two ATP and a byproduct. Bacteria and yeasts use fermentation to get their needed energy. The end products in the case of bacteria may be lactate or alco- hol. For yeasts used in baking breads, the end product is ethyl alcohol and carbon dioxide.

Inside the Mitochondria Contrasting with glycolysis, which takes place in the cyto- plasm, the next three phases of cellular respiration happen inside the mitochondria.

The second phase, preparatory reaction, occurs in the matrix of the mitochondria. During this phase pyruvate is oxidized, releasing the carbon dioxide we exhale when we breathe. NAD+ gains a hydrogen atom to become NADH. A C2 acetyl group is attached to a coenzyme A (CoA), forming acetyl CoA. All of this activity is preparation for the citric acid cycle.

The third phase of cellular respiration is the citric acid cycle, also called the Krebs cycle. During this phase, the acetyl group is oxidized, releasing more carbon dioxide. NAD+ and FAD accept hydrogen atoms to produce NADH and FADH2. Substrate-level ATP synthesis now occurs, producing ATP. Carefully study Figure 7.7 on page 118.

The final phase of cellular respiration is the electron transport chain, which is located in the cristae of mitochondria. High- energy electrons enter the chain; low-energy electrons leave the chain. In the process, the energy released is used to make ATP. More specifically, electrons are transferred through a system that causes the unbound hydrogen ions to be pushed into the inner compartment of the mitochondrion. Electric gradients then cause the hydrogen ions to be pumped back out of the mitochondrion through a series of reactions that drive the formation of an additional 28 ATP.

From start to finish, the process of aerobic respiration pro- duces a net yield of 36 ATP molecules for every molecule of glucose. Review Figure 7.8 on page 119 to master ideas about the electron transport chain. Study Figure 7.9 on page 120 to see how the organization of mitochondrial cristae allows for the production of ATP by using the enzyme ATP synthase.

Introduction to Biology42

Metabolic Fate of Food How much ATP is produced from metabolism?

n 2 ATP from glycolysis

n 2 ATP from the citric acid cycle

n 32 ATP from the electron transport chain

Your body can also obtain energy from molecules other than carbohydrates. These molecules simply enter the process at different points.

After you complete Self-Check 7, review the material you’ve learned in Assignments 1–7. A good way to review the chap- ters is to reread the summaries at the end of each one. If you find you don’t understand something in the summary, go back to the textbook pages and review the material. When you’re sure that you completely understand the information in Assignments 1–7, complete your examination for Lesson 1.

Lesson 1 43

Self-Check 7 1. The largest energy yield during aerobic respiration occurs after which stage?

a. Pyruvate cycle c. Krebs cycle

b. Electron transport chain cycle d. Glycolysis

2. A molecule of glucose contains

a. 12 carbon atoms, 6 hydrogen atoms, and 6 oxygen atoms.

b. 6 carbon atoms, 6 hydrogen atoms, and 12 oxygen atoms.

c. 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms.

d. 8 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms.

3. What process results in 2 ATP and a toxic end product?

a. Fermentation c. Preparatory reaction

b. Citric acid cycle d. Energy harvesting

4. Besides carbon dioxide, the other end product of cellular respiration is

a. oxygen. c. lactate.

b. water. d. nitrogen.

5. In cellular respiration, the number of ATP molecules produced equals about 40% of the energy

available from a glucose molecule. The remainder of the energy is lost as

a. water. c. heat.

b. pyruvate d. carbon dioxide.

Check your answers with those on page 192.

Introduction to Biology44

NOTES

Genetics

INTRODUCTION Your second lesson consists of six assignments. It covers Part II of your textbook, “Genetics,” Chapters 8–13.

OBJECTIVES When you complete this lesson, you’ll be able to

n Explain the basics of cellular reproduction

n Identify and describe the stages of the cell cycle

n Describe the phases of mitosis

n Describe the cell cycle control system

n Describe and explain the basics of meiosis

n Differentiate between the phases of meiosis and mitosis

n Explain some of the effects of abnormal chromosome inheritance

n Outline and explain Mendel’s laws of inheritance

n Relate the basic concepts of sex-linked inheritance

n Create and/or interpret a Punnett square

n Describe and explain the structures and functions of DNA and RNA

n Discuss issues and practical applications related to DNA biotechnology

n Explain the control of gene expression and some results of control failures

n Explain how lack of genetic control can lead to cancer

n Discuss issues related to counseling for chromosomal and genetic disorders

45

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Introduction to Biology46

ASSIGNMENT 8: CELLULAR REPRODUCTION Refer to the following information as you read Chapter 8 in your textbook.

The Basics of Cellular Reproduction Multicellular organisms have two types of cells: reproductive cells (gamete-producing cells) and somatic cells (all the other body cells of an organism). Somatic cells divide by a process called mitosis, and reproductive cells divide by meiosis. Mitosis aids in the growth and development of an organism, as well as in the replacement of old and injured cells. Mitosis results in two daughter cells, which are genetically identical to each other and to the parent. Meiosis, on the other hand, produces gametes for sexual reproduction. The gametes con- tain half of the number of chromosomes as the parent cell.

Cellular reproduction involves two basic processes: growth and cell division. During the growth phase, a cell duplicates its contents and DNA. During cell division, the cytoplasm and DNA of a parent cell are distributed to two daughter cells. During the growth phase, nuclear DNA appears as chromatin. During cellular reproduction, the DNA sorts itself into chromosomes. Figure 8.2 on page 127 illustrates the levels of chromosome organization.

The Cell Cycle: Interphase, Mitosis, and Cytokinesis The cell cycle consists of two stages: interphase and mitosis. Both of these stages are further divided into smaller phases. The time necessary to complete one cell cycle varies greatly depending on the type of organism and the type of conditions. For example, in bacteria, it may take as little as 20 minutes; in higher plants and animals, it may occur over 12–24 hours.

Lesson 2 47

Figure 8.3 on page 128 summarizes the eukaryotic cell cycle. Note that during interphase the cell increases in mass and duplicates its DNA. It’s the longest portion of the cell cycle and is broken down into three parts:

1. During G1 (gap 1) growth phase, a cell grows and builds proteins, carbohydrates, and lipids.

2. During S (synthesis) phase, the chromosomal DNA is replicated in preparation for nuclear division. After DNA replication, each chromatid is attached to its copy by a centromere. At this point, each duplicated chromosome consists of two identical halves called sister chromatids (see page 127 for chromosome terminology).

3. During G2 (gap 2) growth phase, the cell produces pro- teins necessary for mitosis and then prepares to divide.

After a cell completes interphase, it’s then ready to begin the mitotic (M) phase, or mitosis. During the mitotic stage, both the nucleus and the cytoplasm of a cell divide. The result is a pair of daughter cells that are identical to each other and to the parent cell.

The process of mitosis involves five phases. These phases are clearly explained and diagrammed in Figure 8.5 (plant cells) and Figure 8.6 (animal cells). Carefully study these illustra- tions and review the accompanying material on pages 128–133 until you understand how a cell duplicates itself.

While mitosis involves the division of the nucleus of a cell, cytokinesis involves the division of the cytoplasm. Cytokinesis begins at the end of mitosis, during telophase.

The process of cytokinesis occurs differently in plant and ani- mal cells. In plant cells, a cell plate forms between the two daughter cells (Figure 8.8 on page 132). In animal cells, the cytoplasm is basically pinched in two after an indentation called a cleavage furrow forms in the plasma membrane (Figure 8.7 on page 132).

Introduction to Biology48

The Cell Cycle Control System The cell cycle has a series of checkpoints to make sure that everything is proceeding properly. These checkpoints delay development from one phase of the cycle to the next until everything that should happen in a particular phase has happened. The G1 checkpoint is important because once it’s crossed, the cell is committed to division. In the G1 phase, if all isn’t as it should be, a remedial phase—G0—kicks in to make adjustments. If the cell’s DNA is fatally damaged, the cell doesn’t divide. At the G2 checkpoint, cell mechanisms check to assure that the cell’s DNA has replicated. Figure 8.9 on page 133 illustrates some cell cycle checkpoints.

Both internal and external signals control the cell cycle checkpoints. Internal cell signals are conveyed by enzymes called kinases. External signals include growth factors and hormones that stimulate cells to go through the cell cycle.

In a multicelled organism, cells are constantly dying and being replaced. The programmed chemical process that causes a cell to self-destruct is called apoptosis. Apoptosis and cellular division are essentially opposite processes. Basically, apoptosis serves the purpose of keeping the num- ber of cells in the body roughly constant and removing cells with damaged DNA.

The Cell Cycle and Cancer Cancer is considered to be a disease of the cell cycle and results from errors in the signals that control the cell cycle. Carcinogenesis is the development of cancer and typically occurs over many months or years. Cancer cells are nonspe- cialized and undifferentiated and serve no bodily function. The nuclei and chromosomes of cancer cells are abnormal. As cancer cells multiply, they cluster together as tumors. Review the section in your textbook on pages 136–142 to become familiar with the characteristics of cancer cells and tumors.

Lesson 2 49

Self-Check 8 1. Eukaryotic cells generally rely on a cytoskeletal structure called a/an _______ to pull

chromatids apart.

a. centrosome c. spindle

b. centromere d. aster

2. A tumor that has invaded surrounding tissues is considered to be

a. benign. c. carcinogenic.

b. malignant. d. maligned.

3. In the cell cycle, DNA replication occurs during the _______ interval of interphase.

a. G1 c. S

b. G2 d. cytoplasmic division

4. Which of the following lists the correct order of the stages of mitosis?

a. Metaphase, anaphase, telophase, prophase

b. Prophase, telophase, metaphase, anaphase

c. Metaphase, prophase, anaphase, telophase

d. Prophase, metaphase, anaphase, telophase

5. During which stage of mitosis does the nuclear envelope start to break down?

a. Prophase c. Anaphase

b. Metaphase d. Telophase

6. During _______, the two copies of each chromosome separate from each other and begin to

move to opposite poles.

a. prophase c. anaphase

b. metaphase d. telophase

7. The process by which cancer cells travel through lymph or blood and start tumors in new

locations of the body is called

a. carcinogenesis. c. apoptosis.

b. angiogenesis. d. metastasis.

8. A _______ is a repeating DNA sequence found on the ends of chromosomes that acts as a

“cap” that encourages chromosomal stability.

a. centromere c. growth factor

b. stabilizer d. telomere

Check your answers with those on page 193.

Introduction to Biology50

ASSIGNMENT 9: MEIOSIS AND THE GENETIC BASIS OF SEXUAL REPRODUCTION Refer to the following information as you read Chapter 9 in your textbook.

In asexual reproduction, one parent organism produces off- spring that are genetically identical to the parent. Therefore, asexual reproduction can produce exact clones of the parent organism. In sexual reproduction, offspring inherit one copy of each gene from both a female and a male parent organism. These genes can occur in different forms called alleles, which produce different traits in the offspring. Therefore, offspring produced sexually are different from their parents. Most eukaryotic organisms reproduce sexually. The basic events that occur during sexual reproduction are meiosis, gamete formation, and fertilization.

The Basics of Meiosis Meiosis is a type of cell division in which the number of chro- mosomes is reduced in half from the diploid number (2n) to the haploid number (n). The result of meiosis is four gametes: eggs in females and sperm in males. During meiosis the chromosomes divide once, but the nucleus, and sometimes the cytoplasm, divides twice. In this way, four haploid daugh- ter cells are produced from one diploid parent cell. Later, when fertilization occurs, two haploid gametes combine to form a diploid zygote. This combination restores the diploid condition necessary for the life cycle to continue, as illus- trated in Figure 9.2 on page 148. As the zygote develops, each diploid somatic cell produced has a pair of each type of chro- mosome, one inherited from the mother and one from the father. We call these homologous chromosomes, or homologues. Figure 9.1 on page 147 illustrates the homologous chromo- somes of a human male. Note that homologous pairs of chromosomes are typically the same length. Humans have 22 pairs of autosomes that are the same size and one pair that’s differently sized in males—the sex chromosomes.

Lesson 2 51

The Phases of Meiosis Meiosis occurs in two stages—meiosis I and meiosis II. Each stage has its own prophase, metaphase, anaphase, and telophase. Figure 9.5 on pages 152–153 illustrates the phases of meiosis in an animal cell. Keep in mind what you learned in your study of mitosis so that you can compare and con- trast these two processes.

Meiosis Compared to Mitosis As you’ve already learned, both mitosis and meiosis are processes that cause cells to divide. Mitosis results in two cells that are genetically identical to the parent cell. Meiosis results in four cells that are genetically different and have half the number of chromosomes the parent cell does.

Meiosis I is what makes the two processes different. Specifically, synapsis occurs and results in crossing-over, or the exchange of genetic material between the nonsister chro- matids of homologues during prophase I. During metaphase I, the tetrads of homologues line up at the spindle equator. The homologous pairs then separate from each other and move to opposite ends of the cell during anaphase I. Meiosis II is very similar to mitosis, except the process occurs with haploid cells. That is, DNA replication isn’t repeated before meiosis II. During anaphase II the sister chromatids separate and move to opposite sides of the cell, similar to the way they moved in mitosis. Pages 154–155 in your textbook clearly explain the similarities and differences between these two processes.

Also, notice that the two processes differ in both the location and timing of occurrence. That is, meiosis occurs in the gonads (sex organs) and during certain times in the lives of sexually reproducing organisms. Mitosis occurs in most body cells and more consistently throughout the life cycle.

Changes in Chromosome Number The normal number of human chromosomes is 46. Therefore, a normal gamete (egg or sperm) contains half that number, or 23 chromosomes. But errors may occur during meiosis, such

Introduction to Biology52

as nondisjunction, when chromosomes separate incorrectly. This may result in an egg or a sperm with 22 or 24 chromo- somes. When one of these abnormal gametes is involved in fertilization, the result is a fertilized egg with either an extra chromosome (trisomy) or one chromosome too few (monosomy). Down syndrome, described in your text on pages 156–157, is an example of trisomy 21 because chromosome 21 has three copies of the chromosome instead of two.

Other genetic abnormalities can involve the sex hormones. For example, in Klinefelter syndrome the sex chromosome group is XXY. In Turner syndrome, a female has one sex chromosome only (X). Figure 9.8 on page 156 illustrates the effects of Klinefelter and Turner syndromes.

Lesson 2 53

Self-Check 9 1. How many chromosomes are located in a single human somatic cell?

a. 21 c. 42

b. 23 d. 46

2. _______ occurs in cells especially set aside for reproduction, but not in somatic cells.

a. Mitosis c. Metaphase

b. Meiosis d. Formation of sister chromatids

3. In meiosis, the exchange of genetic material between nonsister chromatids occurs during

a. interphase. c. metaphase I.

b. prophase I. d. anaphase II.

4. The first cell that’s formed when two gametes come together at fertilization is the

a. zygote. c. gametophyte.

b. sporophyte. d. homologue.

5. How many daughter cells result when a cell undergoes the process of meiosis?

a. One c. Four

b. Two d. Eight

6. How many chromosomes are located in a single human gamete cell?

a. 21 c. 42

b. 23 d. 46

7. Which of the following processes occurs during meiosis but not mitosis?

a. Cytokinesis c. Cytogenesis

b. Telophase d. Crossing-over

Check your answers with those on page 193.

Introduction to Biology54

ASSIGNMENT 10: PATTERNS OF INHERITANCE Refer to the following information as you read Chapter 10 in your textbook.

Mendel’s Laws Heredity is the transmission of characteristics from one gen- eration to the next. Variations in heredity produce the visible differences between parents and offspring, or between two offspring of the same parents. During the second half of the nineteenth century, a monk named Gregor Mendel conducted experiments with pea plants to try to determine just how par- ent genes are transmitted to offspring. His experiments tested his idea that the plants inherited two units of information (now called genes) for a trait, one from each parent. Mendel conducted his pea plant experiments in stages:

1. Mendel identified parent plants that he knew to be true-breeding for a particular trait (for example, see Figure 10.1 on pages 162–163). That is, when the plants self-pollinated, the offspring were just like the parent plants and like each other. For example, true-breeding tall plants always produced tall plants; true-breeding short plants produced short plants.

2. Mendel selected a true-breeding plant from each group, for example one that produced tall plants and one that produced short plants, and performed a one-trait test cross between the selected parents. That is, pollen from the male parts of one plant was dusted on the female stigma of the other as shown in Figure 10.2 on page 163. The true-breeding plants were the first generation in his experiments, called the P generation, or parental genera- tion. The hybrid offspring resulting from such a cross Mendel called the F1 generation, or first filial generation. For the plant height example, the F1 generation inherited a trait for tallness from each parent, but Mendel found that all F1 hybrids resembled one parent since the trait of the other parent wasn’t visible.

Lesson 2 55

3. Mendel allowed each F1 hybrid to self-pollinate and pro- duce the next generation, known as the F2 generation. The resulting F2 offspring exhibited the characteristics of both parental forms in the ratio of 3 dominant individu- als to 1 recessive, thus a 3:1 phenotypic ratio. Figure 10.3 on page 164 illustrates the results of a one-trait (monohybrid) cross.

Mendel’s pea plant experiments led to the development of the modern genetics view, which is described on pages 165–166. Familiarize yourself with the main concepts and terminology. Mendel’s research also led to the formation of two important genetic principles:

1. The law of segregation. The four elements of this law are listed on page 165.

2. The law of independent assortment. The two elements of this law are listed on page 167. Figure 10.6 illustrates a two-trait cross and its associated ratio of F2 phenotypes (9:3:3:1).

Note that a Punnett square is used to predict the expected ratio of genotypes and phenotypes resulting from the mating of two organisms. Review the Punnett squares in Figures 10.3 and 10.6 and associated terminology so that you understand the material and know how to complete a Punnett square. Also review Figure 10.8 on page 168 to understand how Mendel’s laws are expressed in meiosis.

Mendel’s Laws Apply To Humans A genetic pedigree may be constructed to show the genetic inheritance pattern for an individual in the context of a fam- ily history. The pedigree can be used to predict the likelihood that a genetic disorder will be passed on to offspring.

An autosomal disorder is one that involves any chromosomes except those that determine a person’s gender. An autosomal recessive disorder occurs when an offspring inherits two recessive alleles from either heterozygous or homozygous recessive parents, as shown in Figure 10.9 on page 169.

Introduction to Biology56

Autosomal dominant disorder occurs when an offspring inher- its either two dominant alleles or one dominant and one recessive allele from its parents (see Figure 10.10).

X-linked recessive disorders occur when a recessive allele on an X chromosome is inherited from a parent. This recessive allele is expressed more often in male offspring than in females, since males have only one X chromosome. A dominant allele on the other X chromosome in female offspring often masks the recessive allele. Common examples of X-linked recessive disorders are color blindness and hemophilia A.

On pages 170–172 of your textbook are brief summaries of several autosomal disorders, such as cystic fibrosis, sickle cell disease, and Huntington disease.

Beyond Mendel’s Laws Mendel’s laws are correct, but they’re insufficient in explain- ing the nature of genetic inheritance. In modern times, we now understand that an individual’s genotype, or genetic makeup, must be considered as an integration of all the genes. That is, some patterns of inheritance involve incom- plete dominance, multiple alleles, and polygenes.

n Incomplete dominance occurs when the heterozygote has an intermediate phenotype between that of either homozygote. Figure 10.16 on page 173 illustrates degrees of dominance in humans.

n When more than two alleles control a trait, that trait is called a multiple-allele trait. Figure 10.17 on page 174 shows how multiple alleles work with blood types.

n Polygenic inheritance, the influence of more than two pairs of alleles on a trait, is illustrated in Figure 10.18 on page 174.

Environmental conditions can also influence gene expression. Figure 10.20 on page 176 illustrates different coloration in Himalayan rabbits. This variation is thought to result from differing ambient temperatures—and thus differing body tem- peratures. In human populations, insufficient nutrition during childhood can cause people to be short despite a genetic disposition for tallness.

Lesson 2 57

When a single gene has multiple effects, one mutation can affect many parts of the organism, causing a disease syn- drome. Such a pattern is called pleiotropy. Review Figure 10.21 on page 176 for an example of pleiotropy called Marfan syndrome, which can impact bones, the heart, blood vessels, eyes, lungs, and skin.

Genes at different locations on the same chromosome are linked together in groups—that is, they don’t sort independ- ently of one another during meiosis. These linkage groups can be disrupted by crossing-over. This factor is the basis for genetic recombination in offspring, which produces recombinant gametes. The farther apart two genes are on a chromosome, the greater the chance of crossing-over.

Sex-Linked Inheritance Some traits unrelated to gender are controlled by genes car- ried on the X chromosome. These are called X-linked genes. Therefore, an X-linked gene can produce a pattern of inheri- tance that differs from what one may expect from the genes on the 22 pairs of autosomes. For the sex chromosomes, males have one X chromosome and one, shorter, Y chromo- some that carries fewer genes than the X chromosome. For this reason, males have one copy of each gene that’s carried on the X chromosome. Therefore, males exhibit the phenotype of each single X-linked gene inherited from their mothers. For this reason, X-linked disorders are more common in males.

Introduction to Biology58

Self-Check 10 1. If an individual’s alleles for a certain trait aren’t identical, the individual is said to be

a. true-breeding. c. heterozygous.

b. homozygous. d. recessive.

2. Assume that the allele for curly hair dominates the allele for straight hair. If a homozygous

man with straight hair marries a homozygous curly-haired woman, we would expect their

children to display which phenotypes?

a. All would have straight hair.

b. All would have curly hair.

c. Three out of four would have straight hair.

d. One out of four would have straight hair.

Use the example Punnett square results from a two-trait test cross shown below to answer

Questions 3–5. Assume that the allele for brown hair (B) dominates the allele for red hair

(b) and that the allele for curly hair (C) dominates the allele for straight hair (c).

3. If two terriers are heterozygous for these alleles, what is the expected phenotypic outcome for

their offspring?

a. 9/16 red curly, 3/16 brown straight, 3/16 red straight, 1/16 red curly

b. 9/16 brown curly, 3/16 brown straight, 3/16 red curly, 1/16 red straight

c. 1/4 brown curly, 1/4 brown straight, 1/4 red curly, 1/4 red straight

d. All will have brown, curly hair.

4. What would result if two terriers are homozygous dominant for both of these alleles?

a. All offspring will be brown with curly hair.

b. All offspring will be red with straight hair.

c. One half of the offspring will be brown with curly hair.

d. One fourth of the offspring will be red with straight hair.

Continued

BBCC BBCc BbCC BbCc

BBCc BBcc BbCc Bbcc

BbCC BbCc bbCC bbCc

BbCc Bbcc bbCc bbcc

Lesson 2 59

Self-Check 10 5. If the two terriers produced pups that were reddish-brown with curly hair, then

a. brown displays incomplete dominance over red.

b. red displays partial dominance over brown.

c. curly hair displays incomplete dominance over straight hair.

d. a mutation must have occurred.

6. What outcome would you expect if you cross a homozygous red tulip with a homozygous

yellow tulip if red is incompletely dominant over yellow?

a. All offspring will be red.

b. One-half of the offspring will be yellow.

c. One-fourth of the offspring will be orange.

d. All of the offspring will be orange.

7. The ability of primroses with the same genotype to express different phenotypes for flower

color is an example of

a. a dihybrid cross.

b. codominance.

c. an environmental effect on gene expression.

d. pleiotropy.

8. Genes that can be passed on to offspring by a female carrier are

a. X-linked. c. recombinant.

b. recessive. d. Y-linked.

9. Testing has identified an autosomal recessive disorder in which the red blood cells are

misshapen and irregular. This person probably suffers from

a. Huntington disease. c. sickle cell disease.

b. hemophilia. d. Marfan syndrome.

Check your answers with those on page 193.

Introduction to Biology60

ASSIGNMENT 11: DNA BIOLOGY Refer to the following information as you read Chapter 11 in your textbook.

DNA and RNA Structure and Function

Structure of DNA

As you learned, genes are found on chromosomes that are composed of DNA molecules and proteins. Deoxyribonucleic acid (DNA) is a long chain of repeating units called nucleotides. Each nucleotide contains a five-carbon sugar, a phosphate group, and one of four nitrogen-containing bases—adenine (A), guanine (G), cytosine (C), and thymine (T). Adenine and gua- nine are two-ringed structures called purines; cytosine and thymine are single-ringed structures known as pyrimidines.

DNA consists of two strands that spiral around each other in a structure called a double helix. The two strands are held together by hydrogen bonds and complement each other with regard to the arrangement of the bases. A and T always pair together via two hydrogen bonds, and G and C always pair together with three hydrogen bonds. As a result, if the base sequence of one strand of a DNA molecule is known, you can easily figure out the base sequence of the other strand. Figure 11.5 on page 188 offers you an illustration of DNA structure and complementary base structure.

Replication of DNA

Recall that chromosomes are copied prior to cellular division, during the S phase of interphase, in a process called DNA replication. The process begins with the two strands of DNA becoming separated by the enzyme helicase. Both of the separated strands are then used as templates to build new DNA molecules. Nucleotides in the nucleus pair up with their complementary base pairs and form new strands with the help of an enzyme called DNA polymerase. Each new DNA

Lesson 2 61

molecule is composed of one old strand and one new strand, as described by the semiconservative model. Figure 11.6 on page 189 explains and illustrates DNA replication.

RNA Structure and Function

Ribonucleic acid (RNA) is a single-stranded molecule that con- sists of nucleotides arranged in a long chain. It contains a five-carbon sugar called ribose, a phosphate group, and four nitrogen-containing bases—adenine, guanine, cytosine, and uracil (U). Figure 11.8 on page 190 illustrates the structure of RNA.

There are three types of RNA:

1. Messenger RNA (mRNA) carries information coding for protein synthesis from DNA to the ribosomes of the cell.

2. Transfer RNA (tRNA) carries the required amino acids from the cytoplasm to the ribosome for protein synthesis. In the ribosome, tRNA helps to arrange the amino acids into the proper sequence for the synthesis of a protein.

3. Ribosomal RNA (rRNA) makes up about 80 percent of the total RNA. Molecules of rRNA bind with certain proteins to form a complex called a ribosome. A ribosome is a complex that reads the mRNA to link amino acids into the specified proteins.

Gene Expression Gene expression occurs as triplet codes of amino acids, called codons, are transcribed and then translated to produce the very wide range of proteins used in multicellular organisms. During the process of transcription, a DNA template strand is used to form an mRNA copy of a gene. Figure 11.11 and accompanying text on page 193 describe this process. Newly formed mRNA molecules must undergo processing before they can be used. Figure 11.12 illustrates mRNA processing from DNA.

Introduction to Biology62

The second phase of gene expression is translation, which uses various enzymes as well as mRNA, tRNA, and rRNA. Figure 11.13 on page 194 illustrates tRNA structure and function. Ribosomes, the site where translation occurs, are composed of rRNA molecules and proteins.

DNA translation has three phases: initiation, the elongation cycle, and termination. After studying this material in your textbook, review Figures 11.14 and 11.15 on page 195. Figure 11.14 illustrates how initiation involves the organiza- tion of a ribosome. Figure 11.15 illustrates the elongation cycle, which also relates to ribosome configuration. Termination occurs at a codon that means “stop.” Study Figure 11.17 on page 196, which summarizes the processes involved with gene expression in eukaryotes.

Lesson 2 63

Self-Check 11 1. Which type of RNA carries the instructions for building proteins?

a. mRNA c. rRNA

b. tRNA d. xRNA

2. Which one of the following bases occurs only in RNA?

a. Thymine c. Uracil

b. Cytosine d. Adenine

3. In DNA replication, one of the two old strands of DNA remains as it was. Therefore DNA

replication is called

a. semiconservative. c. templative.

b. unwinding. d. template redundant.

4. The Watson and Crick model of DNA led to the discovery of

a. messenger RNA. c. X-ray diffraction.

b. complementary base pairing. d. consequential pairing.

5. Which one of the following examples is the correct base pairing for DNA?

a. A-C, G-T c. A-G, C-T

b. A-T, G-C d. A-A, C-C, G-G, T-T

6. During DNA replication, enzymes called DNA _______ help fill in the gaps between the

portions of replicated DNA to form a continuous strand.

a. polymerase c. ligase

b. replicase d. lactase

7. Which of the following strands of DNA is a complement to T-A-G-G-T-C-A?

a. G-C-T-T-G-A-C c. A-T-C-C-A-G-T

b. C-G-A-A-C-T-G d. A-T-G-G-A-G-T

8. In the context of gene mutations, if a codon triplet makes no sense in respect to any protein

used by the organism, it’s called a _______ mutation.

a. transposon c. transgenic

b. point d. frameshift

Continued

Introduction to Biology64

Self-Check 11 9. The sequence of all of the base pairs that compose the genes and intergenic DNA segments of

an organism is called a

a. DNA sequence. c. DNA fingerprint.

b. proteome. d. genome.

10. _______ is a DNA sequence that controls transcription in a prokaryote.

a. A repressor c. An operon

b. Polymerase d. A cloning factor

11. Loosely packed chromatin in eukaryotic cells is called

a. a nucleosome. c. an operon.

b. euchromatin. d. heterochromatin.

12. In eukaryotes, transcription _______ are DNA-binding proteins that assist RNA polymerase to

bind to a promoter.

a. activators c. enhancers

b. factors d. translators

13. In general, a cell-signaling pathway begins when

a. a chemical signal is emitted from a transmitter protein.

b. an end product activates reactions within a cell’s cytoplasm.

c. a chemical signal binds to a receptor protein.

d. a transcription activator reacts to the chemical signal.

Check your answers with those on page 194.

Lesson 2 65

ASSIGNMENT 12: BIOTECHNOLOGY AND GENOMICS Refer to the following information as you read Chapter 12 in your textbook.

Biotechnology Humans have learned to purposefully bring about genetic changes by isolating gene sections, cutting them, and then splicing them together with genes from other species. The genes that interest scientists can be amplified in number in the laboratory to be used for research and practical applica- tions. Figure 12.1 on page 208 illustrates recombinant DNA technology used to produce insulin. Figure 12.2 on page 209 illustrates the polymerase chain reaction, which can be used to produce millions of copies of a DNA segment in a short period of time.

Applications of DNA technology include DNA fingerprinting, as described and illustrated on page 210, and the creation of transgenic organisms. The latter applications of biotechnology have included the successful cloning of a few different ani- mals—most famously a sheep named Dolly.

Stem Cells and Cloning With a few exceptions, like red blood cells, every cell in your body has a nucleus that contains the full DNA menu for your entire body. With this understanding, biotechnology has undertaken practical research into two kinds of cloning as illustrated in Figure 12.4 on page 212. Reproductive cloning is undertaken to produce a genetically exact clone of an organism.

Therapeutic cloning is aimed at producing mature cells of dif- ferent kinds. Beyond research interests, possible objectives include producing tissues for medical treatments of spinal cord injuries and conditions like diabetes. Several methods are used to carry out therapeutic cloning. The most commonly

Introduction to Biology66

used method involves isolation of embryonic stem cells and treatments that cause them to specialize and become muscle cells, nerve cells, or red blood cells. Embryonic stems cells are totipotent, which means they have the potential to develop into any cell type found within an organism. Another method used in therapeutic cloning involves the use of adult stem cells that are found in many of the organs of adults. Adult stem cells are multipotent, which means they’ve begun the process of specialization and therefore can develop only into certain cell types.

Biotechnology Products Transgenic organisms are naturally occurring organisms that have been genetically modified for various purposes. Currently, transgenic organisms include bacteria, plants, and animals as discussed on pages 213–215. Some products from bioengi- neered bacteria are insulin and human growth hormone. Plants can be made both insect and herbicide resistant. They can also be made more nutritious and sturdy. Scientists can insert genes into animals that cause them to produce sub- stances that they normally don’t, or even make their organs suitable for human transplant.

Genomics and Proteomics Current DNA research concerns genomics, the study of the genomes—the sequence of genes and intergenic DNA sequences—of humans and other organisms. Slight differences in the base sequences of genes result in each individual being genetically and physically unique (except for identical twins). Researchers involved with the Human Genome Project were able to determine the number, location, and sequence of genes contained within our DNA. Researchers can now com- pare the genome of humans to those of other species. Results from these studies have revealed that the genomes of verte- brate and even some invertebrate species are similar to one another. Figure 12.7 on page 217 illustrates the comparative study of human and chimpanzee genomes to discover that the genes for speech, hearing, and smell may have influenced human evolution.

Lesson 2 67

The human genome contains approximately 25,000 genes that code for about 100,000 different proteins, which are called the human proteome. Proteomics studies the structure and function of these proteins and how they work together to influence the expression of genetic traits. Bioinformatics involves the use of computer technologies to research the genome and proteome.

Self-Check 12 1. _______ cloning refers to producing cells that might be used to repair spinal tissue injuries.

a. Nuclear c. Specialized

b. Specific d. Therapeutic

2. _________ act as a carrier for foreign DNA.

a. Vectors c. Grana

b. Enzymes d. Promoters

3. The first step of the _______ process denatures DNA at 95°C to separate the strands.

a. transgenic bacteria cloning

b. recombinant DNA technology

c. DNA fingerprinting

d. polymerase chain reaction

4. _______ is crucial to the development of new drugs.

a. Proteomics c. Genomics

b. Bioinformatics d. DNA synthesis

5. 94% of ________ in the United States are genetically engineered.

a. rice c. tomatoes

b. corn d. soybeans

6. The gene for _______ has been used to create larger fish and rabbits.

a. human growth hormone c. gigantism

b. bovine growth hormone d. equine rapid growth hormone

Check your answers with those on page 194.

Introduction to Biology68

ASSIGNMENT 13: GENETIC COUNSELING Refer to the following information as you read Chapter 13 in your textbook.

Genes and Gene Mutations We know that genes are DNA sequences that code for pro- teins. Variations in a gene are called alleles. These alleles come from mutations, which are a change in the nucleotide sequence. Mutations can be caused by errors in DNA replica- tion, a transposon, or a mutagen. A point mutation changes a single nucleotide. The severity of the result depends on the particular base change that occurs. A frameshift mutation is caused by extra or missing nucleotides, which affects how the entire sequence is read. This type is usually much more severe than a point mutation because all the downstream codons are affected.

Chromosomal Mutations Chromosomal mutations, which can typically be identified using a microscope, may produce a change in chromosome number. There are four types of structural changes that may occur:

1. A deletion may occur when a segment of a chromosome is lost due to some environmental factor such as a viral attack or exposure to some kind of chemical, like a pesti- cide. Figure 13.3 on page 223 provides an example.

2. A duplication occurs when a gene segment is repeated on a chromosome. The result is that the person has more than one allele for a trait. This concept is illustrated in the Figure 13.4 example on page 224.

3. A translocation occurs when a broken piece of a chromo- some attaches to a nonhomologous chromosome, as shown in Figure 13.5 on page 224.

Lesson 2 69

4. An inversion occurs when a stretch of DNA on the chromosome becomes reversed. Inversions are known to occur in chromosome 15. Figure 13.6 on page 225 pro- vides an example.

Testing for Genetic Disorders Genetic counseling helps parents deal with concerns about the likelihood that a fetus will be impacted by a genetic disor- der. A basic tool of genetic counseling is the karyotype, a visual display of a person’s autosomes and sex chromosomes arranged as pairs. An adult’s white blood cells are normally used to create a karyotype. Different procedures apply for a fetus. In amniocentesis, fluid is drawn from a pregnant woman’s amniotic sac—the membrane that contains the fetus. Fetal cells from the amniotic fluid can be used to create a karyotype. Chorionic villi sampling (CVS) involves drawing tissue samples from the region where the placenta will develop. Cells from the tissue can be used to produce a karyotype. Both of these procedures come with the relatively slight risk of spontaneous abortion.

Tests for genetic disorders employ several different strategies. For example, in search of the risk for Tay-Sachs disease, tests may determine whether a single protein is present or missing. DNA testing may also seek genetic markers like those characteristic of Huntington disease. Figure 13.9 on page 227 illustrates the use of a genetic marker to test for a genetic mutation. New technologies now allow scientists to arrange thousands of mutated alleles onto a tiny silicon chip called a DNA microarray, as illustrated in Figure 13.10. This procedure can be used to test for many genetic disorders at one time. DNA microarrays can also be used to display the entire genome of a person, thereby producing a genetic profile for that individual.

Beyond these noted strategies are procedures for testing a fetus, an embryo, and an egg. A common and popular test of the fetus employs ultrasound, which produces an image of a fetus. This image may show evidence of certain genetic disor- ders. Fetal cells can also be tested for genetic defects. Testing an embryo involves removing a cell once the embryo has six to eight cells (Figure 13.11). Testing eggs is usually carried

Introduction to Biology70

out in the context of in vitro fertilization (IVF) (Figure 13.12, page 230). The polar-body product of female meiosis is removed for testing in IVF—a procedure that doesn’t impact the later development of the egg.

Gene Therapy Gene therapy involves the insertion of genetic material into human cells to treat a disorder. Ex vivo techniques in gene therapy involve the genetic engineering of a person’s cells outside the body. Review Figure 13.13 on page 231 to help you understand ex vivo therapy applied to bone marrow.

In vivo gene therapy techniques attempt to alter cells without removing them from the body. This type of treatment is increasingly used in cancer therapy. Figure 13.14 on page 233 shows you sites where ex vivo and in vivo somatic techniques may be applied.

After you complete Self-Check 13, review the material you’ve learned in Assignments 8–13. A good way to review the chap- ters is to reread the summaries at the end of each one. If you find you don’t understand something in the summary, go back to the textbook pages and review the material. When you’re sure that you completely understand the information in Assignments 8–13, complete your examination for Lesson 2.

Lesson 2 71

Self-Check 13 1. A _______ can be used to test DNA samples for known disease-causing mutated alleles.

a. DNA microarray c. genetic marker

b. DNA microchip d. genetic profile

2. Chorionic villi sampling (CVS) involves drawing tissue samples from the region where the

_______ will develop.

a. fetus c. egg

b. placenta d. X chromosome

3. _______ is the process of transferring normal or modified genes into an individual in an

attempt to correct some type of genetic defect.

a. DNA fingerprinting c. Cloning

b. Gene mutation d. Gene therapy

4. A karyotype of a fetus finds that there are three number 21 chromosomes. This child will be

afflicted with

a. Down syndrome. c. chromosomal deletion.

b. Tay-Sachs disease. d. cystic fibrosis.

5. Williams syndrome results when a/an _______ occurs in chromosome 7.

a. translocation c. deletion

b. inversion d. duplication

6. If a codon triplet makes no sense in respect to any protein used by the organism; it’s most

likely caused by a _______ mutation.

a. transposon c. transgenic

b. point d. frameshift

Check your answers with those on page 194.

Introduction to Biology72

NOTES

Evolution and the Diversity of Life

INTRODUCTION Your third lesson consists of six assignments covering Part III, “Evolution,” and Part IV, “Diversity of Life,” in your textbook.

OBJECTIVES When you complete this lesson, you’ll be able to

n Explain Darwin’s theory of natural selection and cite evidence for the theory

n Discuss and explain the processes involved in microevolution

n Describe the factors that are necessary for natural selection to occur

n Differentiate between different types of natural selection

n Discuss the concept of speciation in different environments

n Explain the gradualistic and punctuated equilibrium models of speciation

n Explain the difference between historic mass extinction events and the current one

n Discuss the principles of taxonomy and the classification of species

n Discuss the first forms of life, including viruses, prokaryotes, and protists

n Describe and explain the origins of land plants and their diversity

73

L e

s s

o n

3 L

e s

s o

n 3

Introduction to Biology74

n Discuss the nature of fungi as distinct from both plants and animals

n Outline an overview of the evolution of animals

n Discuss and describe the invertebrates

n Compare and contrast protostomes and deuterostomes

n Discuss and differentiate flatworms, mollusks, annelids, roundworms, and arthropods

n Discuss and differentiate echinoderms and chordates

n Describe the evolution of chordates

n Explain the basic ideas about the evolution of humans

ASSIGNMENT 14: DARWIN AND EVOLUTION Refer to the following information as you read Chapter 14 in your textbook.

Darwin’s Theory of Evolution Evolution, genetic change in a line of descent over time, is responsible for the tremendous diversity of life forms on Earth. The results of countless scientific studies carried out over hundreds of years provide overwhelming evidence in support of the theory of evolution, which has led to its classification by many scientists as the law (or principle) of evolution. The influence of Charles Darwin’s concepts about evolution, par- ticularly the theory of natural selection, radically transformed not only the science of life, but also were catalysts that changed people’s views about the nature of our world.

The theory presumes that present-day organisms have arisen from simpler ancestral organisms. In general, changes in the genetic composition of a population take place through the inheritance of slight variations that occur generation after generation. This results in the development of new character- istics within a species and the eventual formation of new species in a process called speciation.

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Darwin’s Conclusions

In 1831, Darwin was hired as a naturalist aboard a ship called the HMS Beagle. His five-year voyage took him around the world and gave him the opportunity to study species in a great variety of habitats. After returning to England, he studied his extensive notes on the diversity of species encountered during the voyage, as well as the work of prominent geolo- gists and biogeographers of the time. This research allowed Darwin to formulate many ideas about how evolution occurs, and led to the development of his theory of natural selection. Twenty years after his voyage, Darwin published the book On the Origin of Species that presents his work. The first section of the chapter briefly discusses the HMS Beagle voyage, describes pre-Darwinian worldviews, and also provides exam- ples of observations that led to Darwin’s theories. Also note the section on pages 243–245 that mentions another impor- tant naturalist, Alfred Wallace, who proposed ideas similar to Darwin after voyages in the South Pacific.

Natural Selection and Adaptation

Natural selection is the process by which organisms develop adaptations to their environment, and is the mechanism that results in evolution over many generations. For natural selec- tion to occur, the following conditions must be met:

1. Variation exists between individuals and is heritable. Specifically, variation among individuals is due to genetic variations that are passed to offspring from the parent organisms.

2. The number of individuals in a population remains more or less stable despite more offspring being produced than the environment can support.

3. Competition exists between organisms for limited resources like food, water, nesting sites, and shelter. Individuals with favorable variations have a better chance of survival and therefore increased reproductive success, or fitness.

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4. The advantageous traits are passed from generation to generation with organisms becoming better suited, or adapted, for survival in their environment. Over a long period of time, organisms evolve via the process of natu- ral selection.

Since natural selection is based on genetic differences and is influenced by a constantly changing physical environment, it’s an ongoing process with no endpoint. Organisms are continually tested by these changes. New advantageous mutations will occur and be selected in response to the environment. After a period of time, the resulting organisms may appear so different from the original species that a new species evolves. Pages 242–244 provide some information on the theory of natural selection, the mechanism that brings about evolution.

Evidence for Evolutionary Change Several bodies of data support the idea that species have evolved from very simple to increasingly complex organisms over many millions of years. In particular, four bodies of evi- dence support this view: fossil evidence, biogeographical evidence, anatomical evidence, and molecular evidence.

Fossil Evidence

Most fossils are impressions, or casts, in sedimentary rocks of long-deceased organisms. With a few very early exceptions, the fossil record begins to be nearly continuous beginning some 600 million years ago. From that distant time onward, we’re able to trace a progression of plant and animal species that evolved from earlier ancestors. Modern birds, for exam- ple, have physiological features that relate them to dinosaurs. The fossil record is a rich source of information about ancient species now long extinct. Figure 14.12 on page 246 illustrates a re-creation of Archaeopteryx, an extinct species with fea- tures of both modern birds and ancient reptiles. Figure 14.14 on page 247 illustrates how whales evolved from ancient land mammals.

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Biogeographical Evidence

Biogeography is the study of the distribution of plant and animal species. A primary finding derived from studying the global distribution of plant and animal species is that land regions separated from each other have led to different paths of evolution. Australia, for example, long separated from other landmasses, permitted the domination of ecological niches and habitats by marsupials—as opposed to the pla- cental mammals found elsewhere on the planet. Figure 14.15 on page 248 illustrates a few of the marsupials of Australia.

Anatomical Evidence Anatomical evidence takes three general forms:

1. Vestigial (nonfunctional) structures found in some species indicate evolutionary adaptation from earlier ancestors. Some species of snakes, for example, have vestigial structures that once composed pelvises and legs.

2. Homologous structures are very common across many animal species. The upper arm bones (humeri) of birds, cats, humans, whales, and horses are homologous, as illustrated in Figure 14.16 on page 249. Homologous structures imply common ancestors because they indicate that a single structure changed in succeeding genera- tions to adapt to different uses. As seen in Figure 14.17, the embryos of species with common ancestors follow similar paths of development.

3. Analogous structures may serve the same function but are constructed differently and therefore do not indicate common ancestry. For example, the wings of birds and insects are analogous as to function but their distinct anatomy and construction imply different evolutionary paths.

Molecular Evidence

Nearly all organisms on Earth are composed of the same common elements. All life contains DNA, and all organisms use the same 20 amino acids with the same triplet codes to “spell” proteins. Nearly all living things use ATP as an energy source, and also use many of the same enzymes. Figure 14.18

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on page 250 illustrates the significance of molecular differ- ences between different types of organisms. For example, humans differ from monkeys by one amino acid, from ducks by 11 amino acids, and from Candida yeast by 51 amino acids.

Self-Check 14 1. Which of the following factors is required for natural selection to occur?

a. Organisms are members of the same species.

b. Organisms have the same fitness.

c. Organisms have nonheritable differences.

d. Organisms compete for limited resources.

2. How can you tell a population is evolving?

a. Environmental factors are affecting an individual’s survival.

b. Individuals are reproducing only in particular environments.

c. Over generations, a larger portion exhibits favorable adaptations.

d. Population size is growing rapidly.

3. Humans have a tailbone but no tail. This is a/an _______ structure.

a. vestigial c. elusive

b. analogous d. homologous

4. From the Darwinian point of view, when humans breed cattle for certain traits, they’re

engaged in _______ selection.

a. fitness c. commercial

b. artificial d. population

5. As a result of reading Thomas Malthus on the topic of human population increase Darwin

came up with the concept of

a. selective reproduction. c. speciation.

b. natural selectivity. d. survival of the fittest.

6. Evidence suggests that life’s diversity has come about as the result of very slight differences

in certain genes. This sort of observation is most likely to have arisen through examining

_______ evidence.

a. molecular c. biogeographical

b. fossil d. anatomical

Check your answers with those on page 195.

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ASSIGNMENT 15: EVOLUTION ON A SMALL SCALE Refer to the following information as you read Chapter 15 in your textbook.

Natural Selection As discussed in the previous assignment, natural selection results in a population acquiring adaptations to their envi- ronment and is the mechanism by which evolution occurs over time. As particular phenotypic traits favor adaptation, survival, and reproduction, allele frequencies within breeding populations change from generation to generation. This is the essence of ongoing natural selection. There are three different types of natural selection, as described in your textbook.

1. Directional selection occurs when an extreme phenotype is favored. An example in Figure 15.2 on page 256 shows the increase in the body size of the horse over time. This directional change suggests that environmental changes favored a larger body size. Another example discussed in your text is selection for genetic traits in Plasmodium, the protozoan that causes malaria, that allowed it to survive drug treatments.

2. Stabilizing selection takes place when extreme pheno- types are selected against, thus resulting in average or intermediate phenotypes. This type of selection is most common, since most individuals in a population tend to be well adapted to their environment. See an example in Figure 15.3 on page 257. Another example, discussed on page 258, is human baby birth weight.

3. Disruptive selection occurs when two or more extreme phenotypes are favored over intermediate types. Typically the two unique phenotypes are adapted to different envi- ronments. See Figure 15.4 on page 257 for an example.

4. Another type of natural selection is sexual selection, which describes adaptive changes in either sex that lead to an increase in the ability to attract and secure a mate. Read pages 258–259, which cover sexual selection and other important aspects of natural selection. Colorful plumage in male birds is an example of sexual selection.

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Microevolution For the science of biology, a population is all of the members of a species living and reproducing within a particular area. Microevolution refers to evolutionary changes within a popula- tion. In terms of genetics, all of the alleles and various gene locations within a population make up its gene pool.

Evolution in a Genetic Context

Individual sexual reproduction by itself can’t change allele frequencies. Put simply, a Punnett square for individual breeding couples doesn’t give the proportions (percentages) of alleles in a breeding population over time. Study the explana- tion for this fact on pages 260–261 of your text.

To work out the relative percentages of dominant versus recessive alleles in the genotypes of a reproducing popula- tion, we can apply a version of the binomial equation, p2 + 2pq + q2 = 1. Review pages 261–262 to see how the calcula- tions work out for a selected set of two alleles.

Causes of Microevolution

Your textbook covers the following causes of microevolution:

1. Mutations create the raw material for evolution. Mutations cause genetic variations within a breeding population. While many mutations are either neutral or destructive, some may favor an adaptive advantage in the phenotype of some individuals in a population.

2. Gene flow occurs when alleles are exchanged between migrating populations of the same species. Basically, the interbreeding of two adjacent animal populations tends to work in favor of stable allele combinations and may actually prevent speciation. Figure 15.10 on page 263 illustrates examples of gene flow related to several sub- species of one species of snake.

3. Random mating occurs when males and females mate by chance according to the laws of probability, and not by selection of a certain genotype or phenotype. Nonrandom mating can lead to microevolution. In assortative mating

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people tend to mate with people who have a similar genotype. Tall people tend to marry other tall people, for example. In sexual selection, particular phenotypic traits may increase the likelihood of mating and reproduction. For example, more assertive males in a population may mate more often than less assertive males.

4. Genetic drift refers to the tendency of allele ratios to change simply by chance, especially given a sufficiently long period of time. For example, the genotypes of mem- bers of species that live in separated habitats tend to gradually drift apart—although usually in minor ways only. Figure 15.11 on page 264 illustrates genetic drift.

n A bottleneck effect may occur when some kind of natural catastrophe greatly reduces the size of a species population. The genotypes of the survivors will become dominant; the genotypes of nonsurvivors will be erased. One example is the cheetah, an endangered species that’s suffering from low genetic diversity and the effects of inbreeding. Figure 15.12 on page 265 illustrates the bottleneck effect.

n A founder effect may occur when populations are separated to interbreed more or less exclusively over time. This leads to a higher proportion of rare alle- les, such as those for extra digits, in a population.

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Self-Check 15 1. What mechanism creates new alleles?

a. Independent assortment c. Industrial melanism

b. Random mating d. Mutation

2. If we observe small changes in the frequency of an allele’s appearance in a population’s

offspring due to mutation, natural selection, and genetic drift, we’re observing

a. microevolution. c. genetic equilibrium.

b. mutation rate. d. polymorphism.

3. Gene flow is the movement of alleles into and out of a population as a result of

a. fertilization. c. mutation.

b. migration. d. stabilizing selection.

4. A group of individuals of the same species occupying a given area is a

a. gene pool. c. generation.

b. phenotype. d. population.

5. The genes shared by an entire group and their offspring constitutes a/an

a. gene pool. c. allele frequency.

b. population. d. phenotypic variation.

6. If we’re looking for the proportions of recessive to dominant alleles A and a under the Hardy-

Weinberg equation p2+ 2pq + q2 = 1, and p2 is the frequency of homozygous dominant (A)

individuals, then q must represent the frequency of

a. heterozygous individuals. c. homozygous recessive individuals.

b. random mating. d. homozygous genetic drift.

7. When we see that two or more extreme phenotypes of field mice are favored over any

intermediate phenotype for this species, we’re detecting _______ selection.

a. maintenance c. stabilizing

b. disruptive d. directional

8. If some members of a population exhibit adaptations that increase their ability to attract

mates, _______ selection is occurring.

a. sexual c. stabilizing

b. fitness d. directional

Check your answers with those on page 195.

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ASSIGNMENT 16: EVOLUTION ON A LARGE SCALE Refer to the following information as you read Chapter 16 in your textbook.

Speciation and Macroevolution

Defining Species

A species is considered to be the most basic level of classifi- cation among organisms. Individuals of a species are capable of breeding with each other under natural conditions, but are unable to breed successfully with members of another species. Simply stated, a species is a group of fertile organisms that can interbreed and produce fertile offspring only among themselves. Figure 16.2 on page 270 shows three species of flycatchers. Though similar in appearance, they’re separate species because each reproduces only within their phenotype.

Certain reproductive barriers exist that prevent reproduction attempts and fertilization. For example, prezygotic isolating mechanisms (those occurring before the formation of a zygote) include habitat isolation, temporal isolation related to the time of year individuals mate, behavioral isolation as in the case of different courtship patterns, mechanical isolation, and gamete isolation.

Postzygotic isolating mechanisms (those occurring after a zygote is formed) include such things as the death of non – viable hybrid zygotes and hybrid sterility, in which the adult is reproductively sterile. Mules, the hybrid offspring of don- keys and horses, are an example illustrated in Figure 16.6 on page 272. Another example is called F2 fitness, which occurs when hybrids can reproduce but they can produce only ster- ile offspring. Figure 16.4 on page 271 presents an overview of both prezygotic and postzygotic reproductive barriers.

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Models of Speciation

Speciation is the process by which a daughter species forms from a population of a parent species. This is caused by mutation, natural selection, and genetic drift. There are three ways speciation can occur:

1. In allopatric speciation, some type of physical barrier prevents gene flow between subpopulations of the same species. Reproductive isolating mechanisms begin to evolve as changes occur in the separated populations. Eventually, the changes are so great that the populations can no longer successfully interbreed. Figure 16.7 on page 273 illustrates allopatric speciation of salamanders.

2. In sympatric speciation, a daughter species arises within an existing population with no physical barrier present. This type of speciation has been important in the evolu- tion of flowering plants that engage in self-fertilization. Mutations in gene number sometimes cause no harmful effects, but they keep the plants from being able to breed with others of the same species, and a new species is formed. See Figure 16.8 for an illustration with respect to modern bread wheat.

3. Speciation through adaptive radiation occurs when neighboring populations become separate species even though their territories overlap in a certain area. It’s sometimes difficult to determine whether these popula- tions are actually separate species, or merely subspecies (geographically distinct populations of the same species) since they sometimes produce hybrid offspring where the territories overlap. Figure 16.9 on page 274 illustrates adaptive radiation in the case of Darwin’s famous Galapagos finches.

The Fossil Record Take time to study Table 16.1 on page 276, which presents the geological time scale, major divisions of geological time, and a summary of major evolutionary events that occurred from Precambrian time to the present. This information is explained further on pages 275–279.

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Today, there are two basically opposed ideas about the pace of speciation. In the gradualistic model, illustrated in part (a) of Figure 16.12 on page 277, evolution over time has been steady and orderly. In the punctuated equilibrium model, illustrated in part (b) of Figure 16.12, new species appear suddenly and then remain largely unchanged until they go extinct. When you read the section on mass extinctions, refer again to Table 16.1 to see when these extinctions occurred. These mass extinctions resulted from radical changes due to such things as volcanism, plate tectonics, as well as radically fluctuating atmospheric and climate conditions. Also note the section on page 279 that describes what some scientists call the sixth mass extinction event, happening now, that differs from the others in that it’s human-caused.

Systematics The objective of systematics is the study of the diversity of organisms at all levels of organization. Taxonomy is a branch of biology concerned with identifying, naming, and classifying organisms. The most specific taxonomic hierarchy is the species. The scientific name of a species consists of its genus and species. As you learned in Chapter 1, organisms are classified by genus, family, order, class, phylum, kingdom, and the broadest taxonomic category, the domain. A domain is the most inclusive category of taxonomical classification. Figure 16.15 on page 280 gives you the taxonomic hierarchy for a species of orchid, Cypripedium acaule.

Phylogenetics

Part of the field of systematics involves the tracing of evolu- tionary relationships between species, known as phylogeny. Scientists rely on both the fossil record and on molecular data to analyze various kinds of clues. Figure 16.16 illus- trates the classification of a phylogenetic tree showing the evolution of sheep, cattle, deer, and reindeer from common ancestors. Figure 16.17 on page 282 illustrates the use of molecular data, such as DNA base sequences, to discover the relative evolutionary “distance” between the galago and mod- ern humans.

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Cladistics and Cladograms

The goal of cladistic systematics is determining testable hypotheses about the evolutionary relationships between organisms. A cladogram is a diagram that illustrates phylo – genetic relationships. The logic and procedures for creating a cladogram are illustrated for you in Figure 16.18 on page 283.

Study Figure 16.19 on page 284, which illustrates the differ- ences between traditional, Linnaean classification and cladistic approaches to phylogeny. The differences derive from different assumptions about how to determine traits derived from common ancestors. All of this should remind you that science is an ongoing process.

The Three-Domain System

You’ve already seen that there are different approaches to taxonomic schemes for classifying organisms. Be sure to become familiar with the differences between the traditional five-kingdom system and the newer approach, the three- domain system, which is based on systematics. Figure 16.20 on page 285 allows you to visualize the three-domain system that includes Bacteria and Archaea as Prokaryotes, differenti- ating these organisms from the kingdoms that comprise the Eukaryotes.

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Self-Check 16 1. The evolution of many new species from a single lineage is likely to involve

a. adaptive radiation. c. gametic mortality.

b. anagenesis. d. mass extinction.

2. In _______ evolution, two species acquire traits similar to those of very distantly related

evolutionary ancestors.

a. homologous c. phylogenetic

b. parallel d. convergent

3. Which of the following is a postzygotic isolating mechanism?

a. Habitat isolation c. Hybrid sterility

b. Behavioral isolation d. Gamete isolation

4. The courtship rituals performed by some male birds to attract females of the same species are

an example of _______ isolation.

a. temporal c. behavioral

b. ecological d. mechanical

5. Speciation due to geographic barriers separating populations is called _______ speciation.

a. allopatric c. parapatric

b. archipelago d. sympatric

6. All of the following factors have been implicated in mass extinctions, except

a. continental drift. c. meteorite impact.

b. punctuated equilibrium. d. loss of habitat.

7. Sympatric speciation may occur in plants due to

a. geographic isolation. c. polyploidy.

b. mechanical isolation. d. gametic mortality.

8. Recent advances in the field of systematics have led many scientists to adopt a _______

system of classification of organisms.

a. three-kingdom c. three-domain

b. five-kingdom d. five-domain

Check your answers with those on page 195.

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ASSIGNMENT 17: THE MICROORGANISMS: VIRUSES, BACTERIA, AND PROTISTS Refer to the following information as you read Chapter 17 in your textbook.

Viruses Viruses are tiny noncellular organic systems that have some properties of living things, but they’re not classified as living organisms. Viruses are infectious agents that cause many dreaded diseases of both plants and animals. Common human viral diseases include mumps, measles, chicken pox, and the common cold. A virus consists of a protein coat, or capsid, wrapped around a chromosome of genetic material (either DNA or RNA). Viruses can reproduce only by comman- deering the metabolic machinery of a host cell. Once they infect host cells, viral cycles proceed through five phases called the lytic cycle. Figure 17.3 on page 291 summarizes the lytic cycle as it relates to the lysogenic cycle, in which the virus is integrated into the DNA of the host cell.

Viruses are adapted to plants and animals in distinct ways. Viruses tend to enter plants through damaged tissues and to move about in the plasmodesmata, the cytoplasmic strands that extend between plant cell walls. In animals, viruses tend to behave like the bacteriophages that invade bacteria, except they’re invading eukaryotic cells. On page 292, Figure 17.4 illustrates an infected tobacco plant. On the same page, Figure 17.5 illustrates the reproduction of the HIV retrovirus in an animal cell. A retrovirus has an RNA genome even though it goes through a DNA stage. Figure 17.6 on page 293 illustrates the rather appalling incidence of emerging diseases around the globe—reminding us that viruses tend to evolve as they utilize the nuclear material of host cells.

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Viroids and Prions Unlike viruses, viroids are naked strands of DNA that have been implicated in serious crop diseases. They’re similar to viruses in that they infect cells and direct them to produce more viroids. Meanwhile, recently discovered prions are pro- tein-like particles that act as agents of disease by altering the nature of proteins in host organisms in a destructive direc- tion. Prions can cause diseases such as mad cow disease and also are associated with chronic wasting syndromes in other animal species.

The Prokaryotes The prokaryotes are sorted into two domains, Bacteria and Archaea. Both are simple unicellular creatures that lack membrane-bounded nuclei. The first cells on Earth were prokaryotes, which were likely preceded by protocells com- posed of biomolecules as described on page 296.

Bacteria

Domain Bacteria is comprised of 400 known genera that are found in practically every environment on Earth, including the human body. As discussed in a previous chapter, DNA of prokaryotes is stored within a nucleoid, not a nucleus. Examine the different shapes of bacteria in Figure 17.9 on page 297, as well as their general cellular structure in Figure 17.10.

Both bacteria and archaea reproduce through binary fission, the splitting of a parent cell into two daughter cells (see Figure 17.11 on page 298). Bacteria may also reproduce by three means of genetic recombination:

n During conjugation, which occurs in closely related species, DNA is passed from a donor cell to a recipient cell through tiny tubes called pili.

n In transformation, fragments of DNA are picked up from surrounding living or dead bacteria.

n In transduction, bacteriophages carry portions of bacter- ial DNA from one cell to another.

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Some bacteria are photoautotrophs (also called autotrophs), which are capable of oxygen-based photosynthesis. Most bacteria, however, are chemoheterotrophs (heterotrophs), which obtain their nutrition from other organisms. Most species of bacteria aren’t harmful, and in fact many are bene- ficial to humans. Humans depend on beneficial bacteria for digestion, as well as decomposers involved with sewage treat- ment and those that break down dead organic matter in the soil. Bacteria are also used to produce food items such as yogurt and pickles, as well as antibiotics. Be sure to read the section on beneficial bacteria on pages 299–301.

Some heterotrophs are pathogenic, and cause a variety of ill- nesses including botulism, tetanus, and Lyme disease.

Archaea

Domain Archaea consists of ancient prokaryotes that are adapted to extreme habitats like those that were more preva- lent on the early Earth. Today, they thrive in oxygen-free environments such as sewage, swamps, and animal guts; salty environments like salt lakes; and hot environments such as hot springs and hot lava rock; as well as highly acidic soils. Types of archaea include methanogens, which release methane into the air, and halophiles, which depend on environments rich in salts. Figures 17.16–17.18, all on page 302, illustrate three typical archaea habitats.

The Protists The protists include all the eukaryotic unicellular organisms that may resemble either animals or plants. They’re primarily aquatic and are widely distributed all over the world in oceans, lakes, and ponds. Because some protists live in very inhos- pitable environments—like deep ocean steam vents—they’re considered to be among the most ancient life forms on our planet. There are three major groups of protists: algae, proto- zoans, and slime and water molds.

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Algae are plantlike protists, which are generally photosyn- thetic. They may be single-celled, or they may cluster in colonies as in the case of red, brown, and green types of algae. Figure 17.21 on page 304 presents an inside view of a Chlamydomonas, an autotrophic green alga. Algal diversity is illustrated in Figure 17.22 on page 305.

Protozoans are categorized by the types of locomotion they employ.

n Ciliates, such as Paramecium in Figure 17.23 on page 306, have hairlike cilia for swimming about to capture food such as bacteria, algae, or other protozoans. Some examples of protozoan diversity are shown in Figure 17.24.

n Amoeboids use pseudopods (false feet) for moving around and capturing prey.

n Radiolarians and foraminiferans are marine amoeboids that form calcium carbonate shells. The accumulation of these shells in sediments leads to the formation of limestone.

n Zooflagellates move about by means of long slender extensions called flagella. Under a microscope, flagella look a bit like whips. They flail about to propel the creature from place to place.

n Sporozoans aren’t motile (mobile) or capable of self- propulsion. They complete part of their life cycle inside specific host cells, and are the cause of many human diseases, including malaria.

Slime molds and water molds resemble fungi in many respects. They’re heterotrophic and form spore-bearing structures. Unlike fungi, however, they produce motile cells during their life cycle. The life cycle of plasmodium slime molds is illus- trated in Figure 17.25 on page 307. Slime molds feed on dead plant matter, and therefore assist with the cycling of nutrients. They also feed on bacteria, providing checks on bacterial populations. Water molds are also decomposers, but can be parasitic on plants and animals.

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Self-Check 17 1. Infectious, disease-causing agents are called

a. bacteria. c. microorganisms.

b. pathogens. d. protists.

2. _______ are self-feeders that depend on sunlight to split water and for the reduction of

carbon dioxide.

a. Chemoautotrophs c. Chemoheterotrophs

b. Photoheterotrophs d. Photoautotrophs

3. A _______ is a rod-shaped prokaryotic cell.

a. bacillus c. spirillum

b. coccus d. flagellum

4. Methanogens, extreme halophiles, and extreme thermoacidophiles are all classified as

a. photoautotrophs. c. archaea.

b. eubacteria. d. protists.

5. In which of these phases of the lytic cycle do we observe the assembly of viral components

within a host cell?

a. Penetration c. Maturation

b. Attachment d. Biosynthesis

6. Complete this analogy: Among protozoans, ciliates are to cilia as _______ are to pseudopods.

a. amoebas c. radiolarians

b. trypanosomes d. sporozoans

Continued

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Self-Check 17 7. Slime molds differ from water molds in that

a. water molds are actually amoebas while slime molds are parasitic.

b. water molds are unique in their capacity to consume plant remains.

c. slime molds are unique in their capacity to consume plant remains.

d. water molds may be parasitic to both plants and animals.

8. Which of the following is not an example of a service provided by beneficial bacteria?

a. Food production c. Bioaccumulation

b. Nutrient cycling d. Bioremediation

9. _______ is the idea that the first eukaryotic cells arose from beneficial associations between

primitive eukaryotes and bacteria.

a. Endomembrane theory c. Ectosymbiotic law

b. Endosymbiotic theory d. Law of symbiosis

Check your answers with those on page 196.

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ASSIGNMENT 18: LAND ENVI- RONMENT: PLANTS AND FUNGI Refer to the following information as you read Chapter 18 in your textbook.

Overview of the Land Plants Plants (kingdom Plantae) are multicelled eukaryotes that are photosynthetic autotrophs. Most plants are vascular, mean- ing they have internal tissues that conduct water and solutes through roots, stems, and leaves. Green plants are the major producers for land ecosystems.

To track the evolution of land plants, we can begin with green algae—water-dwelling photosynthetic organisms including charophytes, which appear to be the common ancestor of land plants. Major evolutionary changes included the devel- opment of vascular tissues, then of seeds, and finally the arrival of the flowering plants (angiosperms) during the age of dinosaurs. The evolution of the different kinds of land plants is described on page 314, and is illustrated in Figure 18.2.

The life cycle of all plants is different from that of animals. As illustrated in Figure 18.3 on page 315, land plants undergo an alternation of generations. Thus plants occur in two differ- ent forms: a diploid sporophyte and a haploid gametophyte. Plants vary in the form taken by each generation.

Diversity of Land Plants The four major divisions in the plant kingdom are as follows:

1. Nonvascular plants, including mosses (bryophytes). These plants are well adapted for growth in moist habitats. A moss’s leaflike, stemlike, and rootlike parts have no vas- cular tissues. Instead, they have threadlike structures called rhizoids for absorbing water and solutes. Bryophytes include mosses, liverworts, and hornworts. Mosses are illustrated in Figure 18.5 on page 316.

2. The vascular plants have roots, stems, and leaves.

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n Seedless vascular plants include club mosses, horse- tails, and ferns. All of these kinds of plants reached heroic proportions during the Carboniferous period 286–360 million years ago. They eventually formed the sediments we now mine as coal. Today, seedless vascular plants include maidenhair, royal, and hart’s tongue ferns—illustrated in Figure 18.7 on page 318. Ferns have true roots, and their vascular tissue includes xylem and phloem. Most ferns are found in wet, humid environments since they require a dependable water supply for metabolism and reproduction. Figure 18.8 on page 318 illus- trates the fern life cycle.

n Seed-bearing vascular plants, gymnosperms, and angiosperms have adapted tissue structures for life in drier climates. They produce seeds that encase their embryonic sporophytes inside a protective coat. (See Figure 18.10 to review basic seed anatomy.) They also produce pollen grains as a means for sperm dispersal in the absence of water. Figure 18.11 on page 320 illustrates the process of pollination. In this process, a male gametophyte pollen grain lands on a female gametophyte and then forms a pollen tube that carries a sperm cell to fertilize an egg cell within an ovule. The resulting zygote becomes the sporo- phyte embryo that’s nourished and protected within a seed.

3. Gymnosperms produce “naked seeds,” seeds with no fruit wall covering. In fact, gymnosperm pollination occurs mostly by wind dispersal of the dry male gametophyte pollen grains. This group includes conifers, cycads, and the ginkgo. On page 321, Figure 18.12 illustrates the ancient cycads, and Figure 18.13 illustrates different conifers.

4. Angiosperms are flowering plants in which the seed is enclosed within a fruit wall. The flowering angiosperms are the most highly evolved and diverse organisms in the plant kingdom. Most coevolved with pollinators such as bees and other insects, which allow the plants to “ship” pollen grains to the female reproductive parts of other

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plants. There are at least 240,000 species of angiosperms across the world. Study Figure 18.15 on page 322 to learn the general parts of a flower, including the petals, the stamens, and the carpel. Figure 18.16 on page 323 portrays the life cycle of a flowering eudicot, illustrating the reproductive mechanisms involved in alternating generations.

The Fungi Fungi are distinct from both plants and animals. Review Table 18.1 on page 326 for an overview of the ways fungi dif- fer from plants and animals. In general, fungi are non-green, heterotrophic organisms that grow in dark, moist habitats. Fungi include mushrooms, molds, and yeasts. Figure 18.20 on page 327 depicts the evolutionary relationships among the different groups of fungi and Figure 18.21 shows several types of fungi. The main body of a fungus is called a mycelium, as shown in Figure 18.22. The chains of cells (filaments) that compose the mycelium are called hyphae. Fungal hyphae create an expanded surface area, allowing them greater effi- ciency in extracting water and nutrients from soils. Be sure to review Figure 18.24 and the accompanying text on pages 328–329 that describe the life cycle of a type of zygospore fungi, black bread mold. Club and sac fungi often produce a fruiting body, or mushroom, following sexual reproduction as illustrated in Figure 18.25 on page 329. Another group of fungi is the chytrids, which are unicellular and motile as shown in Figure 18.23.

Most fungi are saprotrophs, which decompose dead organic matter. Fungi may have mutualistic relationships with other organisms. Lichens, for example, involve a mutualistic rela- tionship between a fungus and photosynthetic organism. Lichens and their variations are illustrated in Figure 18.27 on page 330.

Many fungi have beneficial functions. Mycorrhizal fungi sus- tain a mutualistic, symbiotic association between a fungus and the roots of a young plant, as described on page 331. Some fungi—like mushrooms—are a popular source of food for humans and other animals. Fungi are also used to make beer, wine, and cheese.

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Parasitic fungal pathogens, however, are another matter. Some plant fungal diseases are illustrated in Figure 18.30 on page 332. Several mycoses—diseases caused by fungi—can plague humans. Candida albicans produces the widest vari- ety of fungal diseases. Candida infections are generally called “yeast infections” when they infect women’s vaginas, but Candida infestations can also cause what’s called oral thrush, a common condition in newborns and AIDS patients. In peo- ple with suppressed immune systems, Candida can attack other tissues, including those of the heart and brain.

Ringworm, a cause of athlete’s foot, is a cutaneous (skin sur- face) infection that may appear in other skin areas besides the feet. Figure 18.31 on page 333 illustrates oral thrush and ringworm infections, which are described along with other parasitic fungi on pages 332–333.

Self-Check 18 1. The main body of a fungus is composed of a mass of hyphae called a

a. hypha. c. mycelium.

b. chitin. d. filament.

2. The pollen sacs in the flower of an angiosperm are located in the

a. ovary. c. anther.

b. stamens. d. style.

3. The two halves within a peanut shell are actually

a. sporophytes. c. pollen grains.

b. cotyledons. d. stigmas.

4. Drought-resistant male gametophytes are called

a. ovules. c. pollen grains.

b. conifers. d. seeds.

Continued

Introduction to Biology98

Self-Check 18 5. In vascular plants, _______ conducts water and minerals, while _______ conducts organic

nutrients.

a. lignin, phloem c. phloem, lignin

b. xylem, phloem d. phloem, xylem

6. The most common bryophytes include

a. common mosses and club mosses.

b. liverworts and Irish moss.

c. mosses and ferns.

d. liverworts and mosses.

7. Where does germination take place in a flowering plant?

a. Stigma c. Ovary

b. Anther d. Stamen

8. In terms of numbers and diversity, _______ are the most successful plants.

a. gymnosperms c. ferns

b. angiosperms d. bryophytes

9. Unlike animals, plants undergo _______ and display different forms throughout their life

cycle.

a. changing forms c. generational change

b. alternate formation d. alternation of generations

Check your answers with those on page 196.

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ASSIGNMENT 19: BOTH WATER AND LAND: ANIMALS Refer to the following information as you read Chapter 19 in your textbook.

Evolution of Animals Domain Eukarya, kingdom Animalia contains multicelled organisms with cells arranged into tissues and organs. The more complex animals have their organs arranged into organ systems. All animals are heterotrophic and require oxygen for aerobic respiration. Most are motile at some point during their life cycle, which includes stages of embryonic develop- ment. Study Figure 19.1 on page 338 and view how a frog develops from a single fertilized egg.

Some scientists believe that ancient ancestors of all of the animals now living on Earth appeared all at once at the out- set of the so-called Cambrian explosion. Use Figure 19.4 on page 340 to review the proposed evolutionary tree of animals in terms of molecular data. Pages 340–342 discuss evolution- ary trends in cell specialization and development of the body cavity in different groups of animals. Note the basic charac- teristics that developed along the 600-million-year path to the animals we know today. They include true tissues, which are specialized cells organized for specific functions; radial symmetry, in which the animal is organized circularly; and bilateral symmetry, in which the animal has definite right and left halves (see Figure 19.5, page 340). Protostomes can be distinguished from deuterostomes on the basis of their embryonic development, as illustrated in Figure 19.6 on page 341. Protostomes include flatworms, roundworms, mol- lusks, annelids, and the enormous family of arthropods that includes insects, crustaceans, and spiders. Deuterostomes include echinoderms (starfish and sea urchins) and chordates (creatures with backbone structures).

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Sponges and Cnidarians: The Early Animals Invertebrates are animals that don’t have backbones. They’re separated into different phyla with respect to symmetry, type of gut, type of body cavity, and segmentation. The first groups of invertebrates discussed in your textbook are the most primitive, the sponges and the cnidarians.

Sponges: Multicellularity

Sponges, which belong in phylum Porifera, are multicelled but don’t display any type of symmetry, organized tissues, or organs. There are 800 species ranging in size from less than one inch to several feet. Sponges are filter feeders, and water flows into their bodies through microscopic openings and out through larger openings. Collar cells that line the inside of the sponge trap small food particles. Sponges reproduce sex- ually by releasing sperm into the water. After the eggs are fertilized, a swimming larval stage is formed that will later develop into an adult sponge. Figure 19.8 on page 342 illus- trates the anatomy of a sponge.

Cnidarians: True Tissues

Phylum Cnidaria display true tissues. The phylum includes jellyfishes, the hydra, sea anemones, and corals. The cnidaria have radial symmetry. They’re also famous for tentacles with stinging cells called nematocysts. Two common body forms among these creatures are the bell-shaped medusa and the tube-like polyp. Cnidarians are organized to allow their spe- cialized tissues to cooperate; they also feature a saclike gut for food processing. Figure 19.9 on page 343 illustrates the hydra, sea anemone, the Portuguese man-of-war (one of the many kinds of jellyfish), and corals, which form and live in calcium carbonate shells and produce coral reefs.

Lesson 3 101

Flatworms, Mollusks, and Annelids: The Lophotrochozoans Lophotrochozoans are a group of protostome animals that includes flatworms, mollusks, and annelids. They differ from other protostomes in that they’re able to grow larger without molting.

Flatworms: Bilateral Symmetry

Phylum Platyhelminthes includes a group of animals called flatworms. Flatworms were the first animals to display bilateral symmetry and actual organ systems. Often these organisms are hermaphrodites. That is, they have both male and female reproductive parts. They reproduce sexually by exchanging sperm with another individual. Classes of flat- worms include planarians, which are free-living organisms. As shown in Figure 19.10 on page 344, planarians have many of the features found in animals higher up the evolu- tionary ladder. Some examples of parasitic flatworms, the tapeworm and the blood fluke, are illustrated in Figure 19.11 on page 345.

Mollusks

Phylum Mollusca includes coelomate organisms that are bilat- erally symmetrical, with a fleshy, soft body often enclosed within a shell composed of calcium carbonate. As illustrated in Figure 19.12 on page 345, the mollusk body is composed of three parts:

n The visceral mass or soft-bodied part, which holds the internal organs

n A strong muscular foot that’s used for movement

n A muscular or membranous mantle that drapes over the visceral mass

There are three major classes of mollusks, illustrated in Figure 19.13 on page 346:

1. Gastropods include some 90,000 species of snails and slugs. Most have a spirally coiled shell, although some species have a reduced shell or no shell at all.

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2. Cephalopods include squids, octopuses, cuttlefish, and the chambered nautilus. This class contains the fastest- swimming invertebrates (squids) and the smartest (octopuses). These are the only mollusks to display a closed circulatory system for advanced oxygen uptake.

3. Bivalves include oysters, clams, and scallops. They’re called bivalves because their shells have two halves.

Annelids: Segmented Worms

Phylum Annelida, the segmented worms, are organisms with highly pronounced segmentation as well as bilateral symme- try. Their body plans permit complex internal organs and systems, including nephridia, tubules that collect and excrete waste. The phylum contains earthworms and leeches. Earthworms are valuable aids to soil formation, and some species of leeches are parasitic blood feeders. Figure 19.14 on page 347 illustrates the anatomy of an earthworm.

Roundworms and Arthropods: The Ecdysozoans Another group of invertebrate protostome organisms is the ecdysozoans. These invertebrates differ from lophotrochozoans in that they must periodically molt, or shed, an outer cuticle in order to grow larger. The ecdysozoans include the round- worms and the arthropods.

Roundworms: Pseudocoelomates

Phylum Nematoda classifies a group of nonsegmented worms called roundworms. Roundworms display bilateral symmetry, and the body is usually tapered at both ends. A protective covering called a cuticle surrounds the body. Roundworms are the simplest animals to have a complete digestive system. Most are free-living, but some are parasitic species that do great harm to humans, cats, dogs, cattle, and sheep, as described on pages 348–349. Roundworms are male or female, not both as in the case of flatworms. Their anatomy is illustrated for you in Figure 19.16 on page 348.

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Arthropods: Jointed Appendages

Phylum Arthropoda includes an enormous diversity of species and, in that respect, may be considered the most successful animal phylum. The term arthropod means joint-footed. Extant (living) arthropods include crustaceans (crabs and lobsters), arachnids (spiders, ticks, and scorpions), and the more than one million species of insects.

Six characteristics are considered to have contributed to the success of the arthropods. Carefully study all six of these adaptive-success features on pages 349–350 of your text.

Figure 19.17 illustrates an exoskeleton and jointed appendage in a lobster. Figure 19.18 on page 350 illustrates the meta- morphosis of a monarch butterfly. Figures 19.19 and 19.20 on page 351 give you a look at crustacean diversity as well as assorted arthropods—from the black widow spider to the “living fossil” known as the horseshoe crab. Figure 19.21 and 19.22 on page 352 offers you a short visual tour of the diver- sity of insects.

Echinoderms and Chordates: The Deuterostomes

Echinoderms

Phylum Echinodermata includes sea stars, sea lilies, sea cucumbers, brittle stars, sea urchins, and sand dollars—all of which are illustrated in Figure 19.23 on page 353. The echinoderm body wall contains a number of spines that are used for defense. Most have a well-developed inner skeleton and they usually display radial symmetry, with some bilateral features during larval stages. In spite of having no brain, they have a well-developed decentralized nervous system.

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Chordates

Phylum Chordata (the chordates) is divided into invertebrates and vertebrates. In general, chordates include bilaterally sym- metrical animals that have a backbone composed of either cartilage or bone. There are four distinct features present at some stage of development:

1. A dorsal supporting rod called a notochord, which is a long stiff tissue that supports the body

2. A dorsal tubular nerve cord running parallel to the noto- chord and gut, providing the framework from which the nervous system develops

3. Pharyngeal pouches, openings in the wall of the muscu- lar tube, which serve functions related to feeding or respiration

4. A tail formed in embryos and extending past the anus

Compared to the vertebrate group, the chordate invertebrate group is rather small. It includes tunicates and lancelets, shown in Figure 19.26 on page 355.

Phylum Chordata is further divided into classes, explained on pages 357–358.

n Class Agnatha (jawless fish) includes the hagfish and lamprey.

n Class Chondrichthyes includes cartilaginous fishes like sharks, skates, and rays.

n Class Osteichthyes (bony fishes) is the most diverse and abundant vertebrate class. Illustrations on page 357 offer some images of the different kinds of fishes.

n Class Amphibia includes frogs, toads, and salamanders. Figure 19.30 on page 358 offers some illustrations of the evolution of amphibians.

n Class Reptilia includes turtles, snakes, alligators, and crocodiles. Reptiles are the first vertebrate class to escape dependency on water in their habitat due to development of internal fertilization, tough skin, and amniotic eggs, which have internal membranes that conserve water and protect the embryo. Figure 19.32 illustrates the amniotic egg.

Lesson 3 105

n Class Aves includes birds. These are the only animals with feathers, which are derived from skin and used for flight and insulation, as shown in Figure 19.33 on page 359. Like mammals, birds rely on metabolic heat and a four-chambered heart to maintain body tempera- ture. View some examples of variation in bird beaks in Figure 19.34.

n Class Mammalia includes the mammals—the only organ- isms with hair and mammary glands, which produce milk for their young. Humans are included in this class. Most mammals care for their young for extended periods of time, with adults actively teaching certain behaviors. Female placental mammals develop a placenta, a spongy tissue that delivers oxygen and nutrients to the develop- ing embryo and disposes of its wastes. Placental mammals are illustrated on page 362 in Figure 19.36. Marsupials and monotremes, pictured in Figure 19.35 on page 361, are mammals that don’t have a placenta. Monotremes lay eggs; marsupials give birth to underdeveloped young that mature in the mother’s pouch.

Human Evolution Most evolutionary scientists believe that human evolution begins with prosimians, like the ring-tailed lemur, and pro- ceeds across the spectrum of anthropoids onward to the hominids. Anthropoids include all kinds of New World and Old World monkeys, apes, and humans. Hominids are mam- mals that have an anatomy suitable for standing erect and walking on two feet. Figure 19.37 on page 363 presents the suggested evolutionary tree of primates. Note that the com- mon ancestor of the whole group is closest in appearance to modern lemurs.

The evolution of hominids remains clouded in degrees of mystery, largely because the fossil record is thin and new discoveries keep changing the proposed family tree. Basically, the information depicted in Figure 19.38 on page 364 is what evolutionists propose as the progress of our species through basic stages, including the australopithecines, Homo habilis, and Homo erectus. Read pages 363–367 for a description of

Introduction to Biology106

the various human-like hominins. Virtually all of the early fossil evidence of the human-like hominins has been found in Africa. Homo erectus, however, immigrated out of Africa into Asia and Europe. Compare the different hypotheses on the evolution of modern humans on pages 367–368.

After you complete Self-Check 19, review the material you’ve learned in Assignments 14–19. A good way to review the chapters is to reread the summaries at the end of each one. If you find you don’t understand something in the summary, go back to the textbook pages and review the material. When you’re sure that you completely understand the information in Assignments 14–19, complete your examinations for Lesson 3. First complete the multiple-choice exam on your student portal. Then complete the four-question essay exam that follows Self-Check 19.

Lesson 3 107

Self-Check 19 1. A sand dollar or a brittle star displays _______ symmetry.

a. radial c. bilateral

b. cephalized d. segmented

2. The most diverse and numerous of the vertebrates are the

a. lobe-finned fishes. c. birds.

b. reptiles. d. bony fishes.

3. Sponges belong to phylum

a. Cnidaria. c. Porifera.

b. Platyhelminthes. d. Mollusca.

4. Among cephalopods, the _______ has been found to be highly intelligent.

a. snail c. squid

b. nautilus d. octopus

5. Jellyfish are examples of the _______ body form of cnidarians.

a. polyp c. nematocystic

b. medusa d. planula

6. Among mammals, the spiny anteater is distinctive in that it’s a/an

a. egg layer. c. placental mammal.

b. prosimian. d. marsupial.

7. The first hominid group known to use fire is now called

a. Cro-Magnon. c. Homo erectus.

b. Neanderthals. d. Australopithecines.

8. Free-living (nonparasitic) flatworms are called

a. planarians. c. tapeworms.

b. nematodes. d. flukes.

Continued

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Self-Check 19 9. _______ are animals with repeating segments that exhibit bilateral symmetry.

a. Chitins c. Mollusks

b. Annelids d. Deuterostomes

10. Sea cucumbers, brittle stars, and sea urchins belong to the phylum of

a. arthropods. c. crustaceans.

b. echinoderms. d. mollusks.

11. Sharks and skates are classified as _______ fishes.

a. bony c. cartilaginous

b. ray-finned d. amphibious

Check your answers with those on page 196.

109

ESSAY QUESTIONS You have two examinations for Lesson 3. The first is a multiple-choice examination. The multiple-choice exam comes before this assignment on the student portal and should be completed first. The second part is this essay exam, which follows. Please type your answers into a Word file and name the file with your name and the exam number, 25010400.

Questions 1–4: Answer the following essay questions in 1–2 short paragraphs.

1. Compare and contrast directional selection and disrup- tive selection and provide an example of each.

2. Many pathogenic bacteria species are becoming resistant to antibiotics. Explain how such adaptations can develop through the process of natural selection. (Hint: Relate this example to the conditions that are necessary for nat- ural selection to occur.)

3. What are the major evolutionary trends that developed among major vertebrate groups, specifically those that allowed for the transition from aquatic to terrestrial life?

4. Providing examples, explain how sexual reproduction in plants has evolved to become less dependent on water.

To submit your graded project, follow these steps:

1. Go to http://www.pennfoster.edu.

2. Log in to your student portal.

3. Click on Take Exam next to the lesson you’re working on.

4. Follow the instructions provided to complete your exam.

Be sure to keep a backup copy of any files you submit to the school!

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Structure and Function in Plants and Animals

INTRODUCTION Your fourth lesson consists of ten assignments that together comprise two parts in your textbook. Part V, “Plant Structure and Function,” covers plant anatomy and growth; and Part VI, “Animal Structure and Function,” covers anatomy, body trans- port and maintenance systems, nutrition, defenses against disease, and the control systems as these topics relate to the human body. Lesson 4 covers Chapters 20–29.

OBJECTIVES When you complete this lesson, you’ll be able to

n Identify the structure and function of the different types of plant tissues

n Explain how water is transported through plants

n Discuss plant reproduction and development

n Describe the process of homeostasis

n Describe the human nervous system and the importance of neurons

n Identify and describe the function of hormones in the endocrine system

n Discuss the structure and function of skeletal muscle

n Describe the circulatory system and the characteristics of blood

n Describe and explain basic principles related to human nutrition

n Describe the various components that play a role in the body’s defenses against disease

n Describe the functions of the digestive, respiratory, and urinary systems

n Explain the human senses and the nature of motor functions

n Discuss male and female reproductive systems

Introduction to Biology112

ASSIGNMENT 20: PLANT ANATOMY AND GROWTH Refer to the following information as you read Chapter 20 in your textbook.

Plant Cells and Tissues Plants have three types of specialized tissues:

1. The outside of a plant is made up of a single layer of cells called the epidermis, which consists of closely packed epidermal cells. Epidermal cells exposed to air are covered with a waxy cuticle, which restricts water loss and resists attacks by microorganisms. Specialized guard cells present in the epidermis allow for the open- ing and closing of the stomata. Stomata are like pores. They control the movement of water vapor, oxygen, and carbon dioxide across the epidermis.

2. The ground tissue makes up the bulk of the plant body. It includes three types of simple tissues, illustrated in Figure 20.3 on page 374.

n Parenchyma cells, which have thin walls, are active in photosynthesis and storage.

n Collenchyma cells provide support for primary tissues.

n Sclerenchyma cells are fibrous cells that give stalks their gravity-resisting strength.

3. The vascular tissue of a plant is composed of two types of tissues, illustrated Figure 20.4 on page 375.

n Xylem conducts water and dissolved minerals through the plant body. It also functions as a mechanical support for the plant. The cells of this tissue, called tracheids and vessels composed of vessel elements, are actually dead at maturity and the cell walls interconnect to form pipelines for water flow.

n Phloem conducts sugars and other solutes through- out the plant. The cells, called sieve tube members, are alive at maturity. Sugars traveling through the phloem pipelines are unloaded where there’s cell growth or where food storage is needed.

Lesson 4 113

Plant Organs The above-ground parts of vascular plants consist of the shoot system that includes the stems, leaves, and flowers— while the underground portion is composed of the root system. Roots are specialized structures for the absorption of miner- als and water from the soil. Roots also support and anchor the aboveground portion of the plant. Cellular division within the terminal buds of the shoot and root systems causes them to increase in length during what’s called primary growth. Review the basic anatomy of the shoot and root systems on pages 375 and in Figure 20.5.

Perennial plants are those that can outlast winter because their roots can survive to produce new shoots in the spring. Annual plants survive for one season only.

As described on page 376, flowering plants are divided into two types based on the nature of their embryonic leaves, called cotyledons. Monocots have a single cotyledon in their seeds. Eudicots (dicots) have two cotyledons in their seeds. Figure 20.7 on page 376 illustrates the differences between monocots and eudicots.

Organization of Leaves, Stems, and Roots A leaf is composed of a blade attached to a petiole, the stalk that connects the blade to a stem. Basic leaf structure and compound versus simple leaf types are shown in Figure 20.8 on page 378. The interior of a leaf, shown in Figure 20.9 on page 379, is composed of mesophyll, the tissue that carries out the work of photosynthesis, and leaf veins, which trans- port materials to and from the mesophyll cells. The veins carry water and minerals in and transport sugar out.

There are two distinct regions among mesophyll cells.

n Palisade mesophyll has elongated cells.

n Spongy mesophyll contains irregularly shaped cells surrounded by air spaces. This arrangement facilitates a maximum exposure of cell surface areas for gas exchange and water loss.

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Stems Read pages 378–382 and examine the differences between the growth and structure of woody and nonwoody stems. Nonwoody stems, like those of daisies, are illustrated in Figure 20.11 on page 380. Woody stems include bark, which is composed of cork, cork cambium, cortex, and phloem. Wood like that used for lumber is secondary xylem, which builds up year after year in a tree trunk or branch. Since this buildup follows the sea- sons in temperate climates, we can often estimate the age of a tree by counting the annual rings on a cross section of its trunk. Figure 20.12 on page 381 illustrates the organization of a woody stem.

Roots Both monocot and eudicot roots have the same type of growth zones, with each consisting of several types of specialized tissues:

n Vascular cylinder, consisting of xylem and phloem

n Endodermis, which controls the passage of minerals into the vascular tissue

n Pericycle, which can form lateral roots

n Cortex, which contains starch granules

n Epidermis, which often has root hairs

These tissues are listed and explained on pages 382–384 and illustrated in Figure 20.13. Monocot roots are very similar to eudicot roots, but they don’t produce the secondary growth that forms wood. Also, the tissues of monocots are arranged differently to include a central ground tissue called the pith as shown in the image in Figure 20.14.

Plant Nutrition Nutrients are elements essential for a given organism’s growth and survival. Essential plant elements include oxygen and hydrogen (from water) and carbon (from carbon dioxide). Plants also rely on the uptake of a wide range of different elements dissolved in soil water. Those required in greater amounts are called macronutrients. The others, called micronutrients, make up only traces of a plant’s dry weight. You’ll find a diagram on page 385 that specifies essential macro- and micronutrients for plants.

Lesson 4 115

Plants have special adaptations that aid in the uptake of water and nutrients from the soil:

1. Root hairs, shown in Figures 20.2 and 20.13, are slender extensions of epidermal cells specialized for absorption. A plant may develop millions or even billions of these to increase absorptive surface area during primary growth.

2. Root nodules have a mutualistic relationship with certain bacteria as shown in Figure 20.17 on page 386. The bacteria convert nitrogen to usable forms for the plant, while the plant supplies bacteria with organic compounds produced during photosynthesis. Another mutualistic relationship, called mycorrhizal association, exists between roots and fungi. Basically, certain fungi attach to root cells and break down inorganic matter to release minerals for the plant’s use.

Soil, a medium that’s critical for the growth of most plants, is composed of mineral particles and decaying organic matter called humus. Water and oxygen fill in the spaces between these substances. Soil particles come in three sizes—sand, silt, and clay. The suitability of a particular soil for plant growth depends on the proportions of each of these soil particles. Most plants grow best in loams, which are soils containing equal amounts of sand, silt, and clay.

Transport of Nutrients In plants, water and mineral in solutes are taken up in root hairs and then transported upward in xylem. The mech- anism by which water and minerals travel in xylem is called the cohesion-tension model, illustrated in Figure 20.18 on page 387. Transpiration is also involved in the transport of nutrients. Transpiration is controlled by the stomata in leaves. As dry air crosses a leaf surface when stomata are open, water in the plant evaporates into the air. The evapora- tion creates a tension that’s sufficient to draw water upward from the root hairs, through the xylem and onward into the atmosphere. At least 90% of the water taken up by root hairs evaporates from leaves.

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Self-Check 20 1. The centrally located ground tissue of a eudicot stem is the

a. pith. c. cortex.

b. endodermis. d. pericycle.

2. Of the following types of simple plant tissues, the _______ has a number of commercial uses.

a. eudicot c. sclerenchyma

b. collenchyma d. phloem

3. The _______ is the plant tissue in which photosynthesis occurs.

a. sieve tubes c. mesophyll

b. xylem d. phloem

4. Which of the following is not a trait of a monocot plant?

a. Two cotyledons

b. Parallel leaf veins

c. Vascular bundles scattered in stem

d. Flower parts number in threes

5. In the process of _______, the evaporation of water creates a tension that draws water

upward from the root hairs.

a. cohesion c. transpiration

b. adhesion d. mycorrhizal association

6. What is the function of the root cap?

a. Growth c. Reproduction

b. Absorption d. Protection

7. _______ is a secondary form of xylem that builds up year after year.

a. Wood c. Cork

b. Bark d. Cork cambium

8. _______, which help plants “fix” needed nitrogen, are located in root nodules.

a. Fungi c. Stems

b. Bacteria d. Cotyledons

9. Cellular division in the _______, located on the end of each shoot and root, results in an

increase in length.

a. internode c. lateral bud

b. node d. terminal bud

Check your answers with those on page 197.

Lesson 4 117

ASSIGNMENT 21: PLANT RESPONSES AND REPRODUCTION Refer to the following information as you read Chapter 21 in your textbook.

Plant Hormones In flowering plants, different classes of hormones are associated with specific responses. There are five currently recognized groups of plant hormones.

1. Auxins soften cell walls to allow growth. They’re pro- duced in the apical meristem located in the terminal bud of the shoot system as well as in the root tip. Auxins are found in young leaves as well as in flowers and fruits. Auxins inhibit lateral bud growth in the vicinity of the root tip. This process is called apical dominance. Branches can be clipped to encourage further bud growth, as shown in Figure 21.3 on page 394. When a plant is exposed to light from one side, auxin moves to the shady side, causing the leaves on the shady side to elongate and therefore bend toward the light source, as illustrated in Figure 21.2 on page 393.

2. Gibberellins are growth-promoting hormones that are normally found in seeds. Applied externally, they encour- age dwarf plants to grow by elongating leaves and stems. The effect of gibberellins is illustrated in Figure 21.4 on page 394.

3. Cytokinins are hormones that promote cell division. Cytokinins, if applied to plants, can prevent senescence and restore aging leaves, as well as encourage new leaf growth. In overall plant metabolism, cytokinins work interactively with auxins, given the relative acidity of the plant environment, to promote or retard plant growth. A correct ratio of the two hormones is best.

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4. Abscisic acid (ABA) is produced by any plant tissue that contains chloroplasts as well as in monocot endosperm and roots. ABA is sometimes called the plant stress hor- mone because it maintains the dormancy of seeds and buds and closes off stomata. In general, “stress” means cold or adverse weather. The closing of stomata is a spe- cific response to water stress under drought conditions. Effects of abscisic acid are illustrated in Figure 21.5 on page 395.

5. Ethylene is a gas that moves freely in the air. It works with other plant hormones to produce varying effects. One of these effects is the hastening of fruit ripening. Ripening bananas and other fruits give off ethylene. Study Figure 21.6 on page 396 to learn about the effects of ethylene. Note that one of them is abscission—the falling off of leaves.

For an overall review of these five main plant hormones, con- sult Table 21.1 on page 396.

Plant Responses

Tropisms

Plants are able to respond to their changing environment. For example, stomata open quickly in the presence of light and plants turn toward a primary source of light through growth mechanisms. Differential growth in plants is called tropism. Phototropism causes plants to turn toward light; gravitropism causes plant stems to curve away from gravity.

Photoperiodism

In some plants, flowering occurs in response to the ratio of light to darkness over a 24-hour period. In a given plant, this ratio is its photoperiod. With regard to photoperiod, plants can be divided into one of three different groups:

n Short-day/long-night plants

n Long-day/short-night plants

n Day-neutral plants

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Figure 21.9 on page 398 contrasts length of darkness photo – periods in cocklebur, a short-day plant, and clover, a long-day plant. To the extent that plant responses are con- trolled by the photoperiod, they rely on phytochrome—a blue-green leaf pigment.

Sexual Reproduction in Flowering Plants Most plants reproduce sexually by alternating the production of sporophytes, the spore-producing bodies, with the produc- tion of gametophytes, gamete-producing bodies. A sporophyte forms in the vegetative body composed of roots, stems, leaves, and flowers. The gametophytes form in the male and female floral parts. Figure 21.11 on page 400 summarizes the alter- nation of generations in flowering plants.

As flowers form, they differentiate into nonfertile parts, the sepals and petals, and fertile parts, the stamens and carpels. Stamens are the male reproductive parts and are made up of anthers on a long stalk called a filament. The anthers contain pollen sacs. Haploid spores form in the anthers and give rise to the male gametophytes, which are the pollen grains. The female reproductive structures are the carpels. A carpel is composed of a stigma, a style, and an ovary where an egg develops. Review the anatomy of a basic flower in Figures 21.12 and 21.13 on page 401.

Pollination is the transfer of pollen grains from an anther to a stigma. The pollen grain then germinates and develops into a pollen tube that grows down into the ovary, carrying the sperm nuclei with it. Double fertilization occurs, and a diploid zygote forms along with the nutritive tissue needed to sustain it. These two structures form a seed. While the seeds are forming, the ovaries begin to develop into fruits, which help to protect and disperse the seeds. Figure 21.15 on page 402 illustrates the life cycle of flowering plants. Figure 21.17 on page 404 illustrates the development of a seed in a eudi- cot. Check Figures 21.20 and 21.21 and accompanying text on page 406 to review some of the differences between mono- cots and eudicots in their patterns of seed germination.

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Asexual Reproduction and Genetic Engineering in Plants Asexual reproduction in flowering plants can be thought of as an alternative option. Plants contain nondifferentiated meristem tissue. The cells of this tissue routinely reproduce asexually. For example, white potatoes are actually stem extensions. Each eye of the potato is a bud that can generate a new potato. Indeed, potato fields are seeded by planting buds. Sweet potatoes are modified roots, and sections of the root can be planted to produce sweet potatoes. Examine Figure 21.22 on page 407 for examples of asexual reproduction.

Plant cells are totipotent. That is, each plant cell can, in prin- ciple, become an entire plant. Thus, plant cells can be cultured, or developed, as illustrated in Figure 21.23. Today, tissue cultures are widely used in the genetic engineering of plants.

Genetically modified plants (GMPs) are also called transgenic plants. Today, the modification of plants to encompass desir- able genetic traits is a very big global business. And since the commercial potential of genetically modified plants is very large, there are also very large concerns among many people about what’s sometimes called “Frankenfood.” The concerns mainly have to do with unintended consequences of geneti- cally modified corn, wheat, tomatoes, and so on. However, the long-term effects of GMPs aren’t presently clear. Pages 409–410 discuss this controversial topic.

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Self-Check 21 1. _______ is the so-called stress hormone in plants.

a. Abscisic acid c. Ethylene

b. Cytokin d. Auxin

2. The most leaflike part of a flower is called the

a. petal. c. stigma.

b. sepal. d. anther.

3. Initially, a pollen grain is an immature male gametophyte made up of two cells. One of these

cells will become a pollen tube, and the other will become

a. an embryo sac. c. sperm.

b. an ovule. d. a pollinator.

4. Which of the following groups represents the female parts of a flower?

a. Pollen grains, anther, style c. Stigma, ovary, filament

b. Ovary, style, stigma d. Anther, filament, stamen

5. Commercially grown tomatoes are often ripened by treating them with

a. cytokinins. c. auxins

b. ethylene. d. gibberellins.

6. Plants growing upward even in the absence of light are exhibiting a type of

a. thigmotropism. c. gravitropism.

b. phototropism. d. mechanical stress.

7. To say that plant cells are totipotent is to say that

a. they’re composed of nondifferentiated meristem.

b. each plant cell is devoted to vegetative propagation.

c. they’re capable of phototropism.

d. each plant cell can become an entire plant.

Check your answers with those on page 197.

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ASSIGNMENT 22: BEING ORGANIZED AND STEADY Refer to the following information as you read Chapter 22 in your textbook.

The Body’s Organization The cells of most animals interact at three levels of organiza- tion. Namely, tissues are combined into organs, which are components of organ systems. Review Figure 22.1 on page 415 to visualize this idea. Tissues are groups of similar cells performing particular functions—like motility or respiration. There are four major types of tissues: epithelial, connective, muscular, and nervous. The classes of tissues, as well as their relationships to organs and organ systems, are illus- trated in Figure 22.2 on page 416.

Epithelial Tissue Protects

Epithelial tissue covers all the outer surfaces of the body and also lines the body cavities. Although the primary function of epithelial tissue is protection, it also performs other func- tions. Based on these functions, the cells differ in shape. Use Figure 22.3 on page 417 and 22.4 on page 418 to help you differentiate among the different shapes and functions of epithelial tissue cells.

Connective Tissue Connects and Supports

Connective tissue is the most abundant and widely distrib- uted type of animal tissue. There many varieties of connective tissue depending on the bodily functions with which they’re associated. In general, connective tissues are connected in a noncellular material called a matrix. The matrix may be fluid, semifluid, or solid as in bones. Read pages 419–420 for a description of each of the various types of connective tissues, and also view Figure 22.5.

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n Loose connective tissue, like that which lies under the skin to provide elasticity, contains fibers that are loosely arranged in a semifluid substance. It’s composed of cells called fibroblasts that produce a matrix of collagen and elastin fibers that can stretch and then return to their original shape.

n Adipose tissue, a type of loose connective tissue, is com- posed of large, tightly packed fat cells. It’s commonly found under the skin and around the heart and kidneys where it stores energy and acts as insulation.

n Dense fibrous connective tissue is found in tendons and ligaments.

n Cartilage is a pliable intercellular material that’s very strong. It’s found in the nose, ears, and parts of the res- piratory system.

n Bone is composed of collagen fibers that are strength- ened by calcium salts. Bones form the animal skeleton, which supports the body and helps allow for movement.

n Blood is also classified as connective tissue because it consists of cells in a matrix.

Blood serves to transport oxygen and nutrients. Blood con- tains three kinds of cells.

n Red blood cells are disc-shaped cells that lack a nucleus. They’re red because they contain the complex iron-based molecule hemoglobin, which serves to transport oxygen to all the cells of the body.

n White blood cells are nucleated and specialized for differ- ent purposes, mainly related to defense against pathogens.

n Platelets are actually fragments of larger cells that are present only in bone marrow. They serve to assist the clotting process in the event of injury.

Figure 22.6 on page 420 illustrates the three main types of blood cells as they move about in protein fluid, called plasma.

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Muscular Tissue Moves the Body

Muscle tissue is composed of cells arranged in parallel arrays. Layers of muscles contract, or shorten, and then relax in a coordinated fashion. This pattern of contraction and relax- ation helps to move the body and body parts. There are three types of muscle tissue:

1. Skeletal muscle, which is attached to bones, functions in moving the body and its parts. This type of tissue is under voluntary control by the nervous system.

2. Cardiac muscle is present only in the heart. It allows for the contraction and relaxation of heart tissue, which pro- vides for the flow of blood throughout the body.

3. Smooth muscle is present in the walls of the stomach, bladder, lungs, and other internal organs. The contrac- tions of smooth muscles are slower than those in skeletal muscle and are responsible for gut motility, bladder emptying, and other organ functions. Smooth muscles normally function involuntarily.

Figure 22.7 on page 421 illustrates the types of muscular tissue.

Nervous Tissue Communicates

Nervous tissue conducts impulses throughout the body, coordinating body movements and organ functions. The workhorse of all nervous tissue is the neuron, which is illus- trated in Figure 22.8. Neurons, in turn, are supported by neuroglia cells—in a ratio of about 9 to 1. About half of the volume of the brain is made up of neuroglia cells. You’ll be learning quite a bit more about neurons and the nervous sys- tem in Assignment 27.

Organs and Organ Systems Pages 423–425 offer an overview of organ systems that you’ll learn in more detail later. The transport systems include the circulatory and lymphatic systems. Maintenance system functions include digestion, respiration, and urinary manufac- ture and disposal. Control systems include the nervous and

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endocrine (hormone) systems. Sensory input and motor output functions are served by the skeletal and muscular systems. Reproduction is served by the reproduction system. Figures 22.9–22.13 illustrate these five basic systems.

Homeostasis Homeostasis is the ability of an organism to maintain a relatively stable internal environment despite changes in its external environment. Homeostasis can be illustrated by a household thermostat. Let’s say the thermostat is set at 72 degrees. Therefore, if the outside temperature drops below 72 degrees, the thermostat turns on the heat, which then turns off when the temperature reaches 72 degrees.

From the thermostat analogy, it’s easy to understand that homeostasis in biology refers to keeping internal body condi- tions roughly constant. It’s also pretty easy to grasp the idea that homeostatic body processes regulate all kinds of things— temperature, fluid level, sodium level, and so on—by negative feedback. Read pages 426–427 for an overview of the various processes involved with maintaining homeostasis within an organism. Figure 22.14 provides a diagram of homeostasis with respect to blood and fluid levels. Figure 22.15 illustrates the general principles of negative feedback mechanisms.

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Self-Check 22 1. _______ connective tissue found in ligaments features large numbers of collagen fibers

packed closely together.

a. Adipose c. Dense fibrous

b. Loose fibrous d. Fibroblast

2. Complete this analogy: Cells are to tissues as organs are to

a. epithelium. c. a specific function.

b. an organism. d. an organ system.

3. Blood is considered what type of tissue?

a. Epithelial c. Muscle

b. Connective d. Nerve

4. _______ epithelial tissue secretes mucus.

a. Pseudostratified c. Squamous

b. Columnar d. Cuboidal

5. _______ feedback mechanisms are predominant in maintaining homeostasis in the body.

a. Primary c. Localized

b. Positive d. Negative

6. Which type of muscular tissue is striated due to the presence of actin and myosin filaments?

a. Skeletal c. Smooth

b. Connective d. Involuntary

7. Schwann cells are a type of neuroglia that surround nerve fibers with a/an _______ sheath.

a. neuron c. myelin

b. adipose d. dendrite

8. The _______ organ system is considered to be one of the body’s maintenance systems.

a. Respiratory c. Cardiovascular

b. Integumentary d. Nervous

Check your answers with those on page 197.

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ASSIGNMENT 23: THE TRANSPORT SYSTEMS Refer to the following information as you read Chapter 23 in your textbook.

Open and Closed Circulatory Systems In some simple animals, such as hydras and planarians, no circulatory system is necessary. See Figure 23.1 on page 433. Other more complex animals have an open circulatory system like that of the grasshoppers, as shown in Figure 23.2a on page 434. All vertebrates and some invertebrates, however, have closed circulatory systems—properly called cardiovascular systems (see Figure 23.2b). Cardio means “heart”; vascular refers to vessels like veins and arteries. Compare the cardio- vascular systems of fishes, amphibians, birds, and mammals in Figure 23.3 on page 435.

Transport in Humans In the cardiovascular system of humans and other vertebrates, a muscular heart pumps blood throughout the body. Study Figure 23.4 on page 436 to identify the basic anatomical fea- tures of this organ. In particular, note the locations of the left and right atria, the left and right ventricles, and the tricuspid and bicuspid valves and study how blood flows through the heart.

To understand the characteristics of the heartbeat, also called the cardiac cycle, review Figures 23.5 and 23.6 and accompa- nying text on pages 437–438. Trace the circuit from the atrial systole to the ventricular systole, to the atrial and ventricular diastole. The regularity of the heartbeat is controlled by an internal pacemaker called the sinoatrial (SA) node.

The heartbeat creates blood pressure that pushes the blood into large vessels called arteries. The blood then flows into smaller arterioles, which branch into even smaller vessels called capillaries. This is where oxygen, carbon dioxide, nutri- ent, and waste exchange take place. Blood flows from the

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capillaries into small venules. From there, large-diameter veins return it to the heart. Pages 438–439 describe and illustrate the various kinds of blood vessels.

A partition (the septum) separates the heart into two cardio- vascular circuits:

1. The pulmonary circuit consists of a short loop that oxy- genates the blood. It leads from the right side of the heart to capillary beds in both lungs, where the blood picks up oxygen. The loop then returns to the left side of the heart.

2. The systemic circuit is a longer loop that begins at the left half of the heart. Its main artery, the aorta, picks up oxygenated blood that flows through arterioles to capil- lary beds in all regions of the body. Veins then deliver the oxygen-depleted blood back to the right half of the heart.

Read page 440 and review Figure 23.9, which depicts the path of the blood through these circuits. Be aware that the whole process begins and ends with the lungs.

Page 442 describes the process of capillary exchange in the tissues of animals, and how nutrients, wastes, and other substances move throughout the various tissues of the body.

The lymphatic system consists of an extensive system of lym- phatic vessels that complement the blood-circulatory system. Lymphatic fluid—called lymph—takes excess fluids from the tissues and returns it to the cardiovascular veins. The lym- phatic system plays a vital role in maintaining the body’s immune system, which you’ll study later in this course. Study Figure 23.10 on page 441 for a sense of the lymphatic- vessel network. Note the location of ducts in the shoulders and thorax where lymph is deposited into the cardiovascular system.

Blood: A Transport Medium As you’ve already learned, blood is a type of connective tissue that carries out many functions. It transports oxygen and nutrients to all of the cells in the body. It carries away meta- bolic wastes and secretions such as hormones. It transports

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cells that fight infections and remove debris from tissues. It also stabilizes body temperature by moving excess heat from muscles to the skin for dissipation.

Blood components consist of plasma plus a number of formed elements. The formed elements include red blood cells, white blood cells, and platelets. You can get an overall view of the components of blood by reviewing Figure 23.13 on page 443. Figure 23.14 on page 444 summarizes the formed elements of blood.

Plasma is mostly water, but it also contains certain ions and proteins. It serves as a transport medium for blood cells and platelets. It supplies water, oxygen, and metabolites to cells and removes nitrogen wastes and carbon dioxide.

Red blood cells, or erythrocytes, transport oxygen for aerobic respiration and carry away some of the carbon dioxide wastes. As previously noted, mature red blood cells don’t have nuclei. Immature red blood cells, formed in bone marrow, do have nuclei. As red blood cells mature, they begin to synthesize hemoglobin—the complex iron-based molecule that can bind with oxygen. Red blood cells live about 120 days before being “recycled”—mainly in the liver and spleen.

White blood cells, or leukocytes, function in daily housekeep- ing by patrolling tissues and engulfing damaged or dead cells and anything recognized as foreign to the body. Many leuko- cytes are located in lymph nodes and the spleen, where they divide to produce armies of defense cells when the body is threatened. Take some time to study the different kinds of leukocytes and think about their specific functions. Doing this will give you a head start in understanding the body’s defenses against disease discussed later in this course.

Platelets, or thrombocytes, are tiny discs formed by the frag- mentation of large cells that are located in bone marrow. Their function is to initiate blood clotting when necessary. Blood contains at least 12 clotting factors. Among these, pro- teins called prothrombin and fibrinogen are deposited into the blood by the liver.

In the event of an injury that damages tissues and blood vessels, platelets hasten to plug the gap, forming a temporary seal. Then, by way of complex reactions, platelets in conjunc-

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tion with injured tissues, release a clotting factor called pro- thrombin activator that creates thrombin. Thrombin, in turn, acts as an enzyme to catalyze further chemical reactions to produce a proper clot made sturdy by fibrin threads. Study Figure 23.15 on page 445 that illustrates the stages of blood clotting.

Self-Check 23 1. Which one of the following organisms has an open circulatory system?

a. Hydra c. Common field mouse

b. Grasshopper d. Planarian

2. The heart of a vertebrate is in contraction during

a. diastole. c. systole.

b. pulse. d. heartbeat.

3. All of the following are formed elements of blood, except

a. platelets c. white blood cells.

b. red blood cells. d. plasma.

4. Venous blood from the superior vena cava enters the human heart at the

a. left ventricle. c. right ventricle.

b. right atrium. d. left atrium.

5. Which one of the following statements is true of antigens?

a. They don’t belong to the body.

b. They’re produced by an antibody.

c. They’re a form of platelet.

d. They release white blood cells.

Check your answers with those on page 198.

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ASSIGNMENT 24: THE MAINTENANCE SYSTEMS Refer to the following information as you read Chapter 24 in your textbook.

Respiratory System Respiration is the process by which animals move oxygen into blood and rid the body of the accumulated carbon dioxide wastes. Figure 24.1 on page 451 illustrates the gas exchange functions of the respiratory system. The respiratory system is pictured in Figure 24.2 on page 452. Figure 24.3 illustrates the ciliated cells of the respiratory passages.

The Human Respiratory Tract

The function of the human respiratory system is to conduct air to and from the lungs. The system is composed of an upper and a lower respiratory tract.

The upper respiratory tract includes the nasal cavities, which are narrow canals separated by a septum of bone and carti- lage. The nasal cavities connect with air-filled spaces called sinuses, which reduce the mass and weight of the skull and act as resonating chambers for speaking and singing. Inhaled air passes from the pharynx through the glottis, an opening into the larynx. The larynx, or voice box, along with the vocal cords, allows us to vocalize.

The lower respiratory tract begins with the trachea, also called the windpipe. The trachea is a four-inch tube that runs from the larynx. It’s lined with cilia that beat upward to drive out dust particles. The trachea divides into two branches called bronchi, which enter the lungs. The lungs are a pair of respi- ratory organs situated on each side of the heart. They’re separated from the abdomen by a muscular partition called the diaphragm. The lungs are smooth, spongy, and, when healthy, pink in color. The right lung is divided into three lobes. The left lung, which is smaller to accommodate the space taken up by the heart, is divided into two lobes. After entering the lungs, the bronchi divide into smaller bronchioles, like a tree branching into thinner branches and then twigs.

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The smallest branches end in clusters of alveolar sacs, each of which contains bunches of alveoli that resemble clusters of grapes. The alveoli are lined with flat epithelial cells that facilitate the exchange of gases from the networks of blood capillaries that surround every alveolus.

Breathing

Breathing involves inhalation and exhalation. Inhalation (inspiration) is an active process in which air enters the lungs. In the lungs, the exchange of gases between the inhaled air and the bloodstream capillaries takes place through the internal lining of alveoli due to different gas concentration gradients. As oxygen is removed from inhaled air, the air in the lungs quickly becomes saturated with carbon dioxide. Exhalation (expiration) is a passive process during normal activity; that is, it’s automatic. During exhalation, air moves out of the lungs. The ribs fall, the sternum sinks, and the diaphragm arches upward. This reduces the volume capacity of the thorax, and air is expelled from the lungs as a result.

Review Figure 24.5 and accompanying text on page 454 for an overview of inspiration versus expiration. Figure 24.7 on page 455 illustrates the neural control of breathing rate. Figure 24.8 will help you understand the processes of gas exchange in human lungs.

Transport and Internal Exchange of Gases

On page 456, Figure 24.10 illustrates the structure of hemo- globin molecules. Note how oxygen bonds to the central iron atom of a heme group. The chemical reactions given in the text on this page should help you understand how carbon dioxide is carried in the bloodstream and how it diffuses into the alveoli during internal gas exchange.

Urinary System and Excretion In complex vertebrates like humans, kidneys are designed to excrete nitrogenous wastes, like urea and uric acid, and help maintain the body’s water-salt balance. In mammals, the kidneys also regulate the acidity (pH) of blood. In all mammals,

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the two kidneys are compact, reddish-brown, bean-shaped structures located on the dorsal (back) wall of the abdominal cavity. The kidneys constantly filter water and solutes (except proteins) from the blood. They reclaim the amount of water and solutes that the body requires, and the rest is excreted as urine. Each kidney is attached to a ureter, a tube that takes urine from the kidney to a muscular sac called the urinary bladder. A single urethra conveys urine from the body during urination. Figure 24.11 on page 457 gives an overview of the functions of the kidneys.

Each kidney has three major parts.

1. The outer region of the kidney, the renal cortex, has a granular texture.

2. The renal medulla is made up of the cone-shaped renal pyramids that lie inside the renal cortex.

3. The innermost part of the kidney is the hollow renal pelvis. There, urine is collected for transport via the ureters to the urinary bladder.

Under the microscope, we discover that each kidney is com- posed of about one million nephrons—the bodies that produce urine. Figure 24.12 on page 457 displays the anatomy of the urinary system. Figure 24.13 on page 458 illustrates the process of urine formation in the nephron. In this illustra- tion, locate the nephron capsule, the proximal tubule, the nephron loop, the distal tubule, and the collecting duct.

Urine formation includes three steps.

1. First, filtration moves small molecules (water, nutrients, salts, and urea) from a blood capillary to the inside of the nephron capsule.

2. Next, during reabsorption, substances from the proximal tubule move into the bloodstream. This is the kidney’s blood filtration system at work.

3. Finally, secretion is the transport of substances into the nephron by means other than filtration. Secreted sub- stances include uric acid, hydrogen ions, ammonia, and drugs like penicillin that are harmful to the body.

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The final sections of this assignment discuss the manner in which animals maintain water-salt balance and pH. Figure 24.14 shows an example for insects, and Figure 24.15 illustrates the way kidney tubules help maintain the water- salt balance in mammals.

Digestive System

Tube-within-a-Tube Body Plan

Some animals, like the jellyfish, have a sac body plan. A single opening acts as both the entryway for food and the exit for wastes. Most animals, including humans, feature the tube- within-a-tube body plan, which has a separate entrance and exit. Figure 24.18 on page 462 presents an anatomical break- down of the digestive systems of earthworms and humans. Basically, the one-way tube plan includes a gut, also called the alimentary canal, with a mouth at one end and an anus at the other. In this system, the wall of the gut is separated from the outer body wall by a coelom. In Figure 24.18a, you can see that the coelom is simply “packing space” for acces- sory digestive organs.

Animals of all kinds can be sorted by their typical diet. Herbivores eat vegetable matter, carnivores depend on meat, and omnivores will eat either plant or animal matter. Humans are omnivores. The mouths and dentition of the different kinds of feeders are illustrated in Figure 24.19 on page 463.

The physiology of the human digestive system includes a number of components:

n The mouth is the entrance to the system where food is moistened and chewed. Digestion begins when the teeth break down food into smaller particles and salivary glands secrete saliva containing digestive enzymes.

n The pharynx is a short but wide space that serves as a common passageway for both food and air; it moves food forward through the system by muscle contraction.

n The esophagus extends from the pharynx to the stom- ach. As food reaches the esophagus, it’s moved along by involuntary, rhythmic contractions called peristalsis.

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n The stomach is a J-shaped sac that expands to a capac- ity of about one liter. Its epithelial lining, the mucosa, contains millions of gastric glands, which secrete hydrochloric acid (HCl). The high acidity of the stomach is ideal for a digestive enzyme called pepsin. Together, HCl and pepsin kill all kinds of potential pathogens while breaking down proteins into peptides. The thick mucus in the stomach and in the intestines protects these organs from acidity and the actions of digestive enzymes. The churning action of the stomach resolves boluses of food into chyme. Figure 24.21 on page 465 displays the anatomy of the human stomach. Figure 24.22 allows you to contrast the human stomach with the chambered stomach of ruminants, such as cows and camels.

n The small intestine, a tube approximately seven meters long, receives the chyme from the stomach. The small intestine is separated into three regions. The duodenum, a C-shaped structure, receives bile from the liver and digestive enzymes from the pancreas. Nutrients are digested and absorbed by way of fingerlike projections called villi. In the ileum, some nutrients are absorbed while unabsorbed material is passed onward to the large intestine.

n The large intestine absorbs water, salts, and some vita- mins. It then stores indigestible material in the form of feces, which eventually leave the body through the anus.

Accessory Organs

Two accessory organs involved in digestion are the pancreas and the liver. In digestion, the pancreas secretes pancreatic juice directly into the duodenum, as shown in Figure 24.23 on page 466. The pancreas acts as both an exocrine gland and as an endocrine gland. In addition to digestive enzymes it also produces insulin, which regulates blood sugar.

The liver is a large organ that has multiple functions, including

n Blood detoxification, or the removal of poisonous sub- stances from the blood

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n Production of plasma proteins

n Bile production for digesting fats

n Production of urea as a contribution to the urinary system.

Figure 24.27 on page 469 presents an illustration of the hepatic portal system, by which products of digestion are absorbed from the small intestine, processed, and passed onward to the bloodstream through hepatic veins.

Self-Check 24 1. _______ breaks up fats through a process of emulsification.

a. Bile c. Pancreatic amylase

b. Trypsin d. Chyme

2. The coelom separates the _______ from the _______.

a. pharynx, mouth c. pharynx, esophagus

b. alimentary canal, mouth d. alimentary canal, body wall

3. What modification to the respiratory system improves oxygen intake in birds?

a. Larger lungs c. Spiracles

b. More surface area in trachea d. Air sacs

4. To allow for gas exchange, the epithelium of an alveolus is snugly adjacent to the epithelium

of a _______, forming a respiratory membrane.

a. hemoglobin molecule c. bronchiole

b. capillary d. pulmonary artery

5. The structure that allows humans to speak is the

a. alveolar sac. c. larynx.

b. pharynx. d. nasal cavity.

Continued

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Self-Check 24 6. Complete this analogy: The villi are to small-molecule nutrient absorption as the large intes-

tine is to the

a. absorption of water and salts. c. production of a bolus.

b. formation of chyme. d. secretion of intestinal enzymes.

7. The _______ stores bile secreted by the liver.

a. pancreas c. small intestine

b. gallbladder d. colon

8. Urine is formed in the

a. urethra. c. liver.

b. kidneys. d. bladder.

9. The use of an artificial kidney is called

a. filtration. c. excretion.

b. hemodialysis. d. dialysis.

10. In the process of urine formation, the movement of small molecules from a capillary to the

inside of a nephron capsule is called

a. secretion. c. reabsorption.

b. absorption. d. filtration.

Check your answers with those on page 198.

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ASSIGNMENT 25: HUMAN NUTRITION Refer to the following information as you read Chapter 25 in your textbook.

Nutrition Nutrition is the process by which food is obtained, prepared, absorbed, and converted into body substances such as carbo hydrates, lipids, proteins, and nucleic acids. Nutritive processes provide the raw materials necessary for the maintenance of homeostasis and life. Macronutrients include carbohydrates, proteins, and lipids. They’re called “macro” because the body needs to consume them in fairly large quantities on a regular basis. Micronutrients, which include vitamins and minerals, are required in small amounts only. Although the human body can sometimes compensate for a nutrient deficiency, a deficiency disorder will eventually develop. Page 477 provides an introduction to diet and nutri- ents. Table 25.1 on page 478 summarizes the classes of nutrients.

The Classes of Nutrients

Macronutrients: Carbohydrates, Lipids, and Proteins

All of the macronutrients are sources of energy. However, each provides energy in somewhat different ways, and each also has other specific functions.

n Carbohydrates are present in foods as sugars, starches, and fiber. Sugars provide more or less immediate sources of energy, but they can present problems if they’re con- sumed in excess. Starches metabolize differently than sugars. Any excess starches can be stored in the body as glycogen. Fiber isn’t digestible, but it’s important for stimulating effective passage of food through the gut.

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n Some lipids called triglycerides (fats and oils) can be stored in the body for use as energy when needed. Others serve as structural components of cells. Another lipid, cholesterol, can be produced within the body and has various functions including formation of steroid hor- mones and vitamin D. Excess cholesterol and certain fatty acids, including trans fats, can increase the likeli- hood of cardiovascular disease. Typically, nutritionists recommend use of unsaturated over saturated fats in the diet (with exception of some plant-produced saturated fats that lower heart disease risk). Food obtained from animals, including meat and dairy products, is higher in saturated fatty acids.

n Proteins are digested and broken down into amino acids that are then reconfigured to produce the thousands of proteins manufactured in the cells. Pages 480–481 dis- cuss how overconsumption of high-protein foods can be harmful.

Micronutrients

Although the body needs small amounts of micronutrients, they’re vital components of a healthy body. Micronutrients help to process the macronutrients, and are essential for growth and good health.

n Minerals are required for a wide variety of physiological functions, including the regulation of biochemical reac- tions. Table 25.4 on page 482 summarizes the functions and food sources of vital minerals. This table also includes conditions that can be caused by either an excess or a deficiency of a given mineral. In this table, notice that the mineral iron is listed as a trace element, which means the body needs less than five grams of this mineral each day. Even so, iron is crucial to the formation of hemo – globin and therefore is a very important part of good nutrition. Problems associated with sodium, a mineral that’s often overused, are described on page 482 with tips for reducing intake.

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n Vitamins have a wide variety of functions, as summarized in Tables 25.6 and 25.7 on page 483. Either too much or too little of a particular vitamin can cause problematic conditions. Note that some vitamins, such as C, E, and A, act as antioxidants that protect and defend the body from potentially damaging free radicals.

Water

Water is a basic requirement for all living organisms. About 60% of the human body consists of water, and this important molecule is part of countless chemical reactions and also helps to lubricate joints, assist with nutrient transport, as well as maintenance of the temperature of the body. The total amount of water that should be consumed daily varies in response to several factors including a person’s activity level, body size, and environmental conditions.

Nutrition and Health The remainder of Chapter 25 presents a simple, practical guide to understanding relationships between diet and health, as well as what it takes to plan a nutritious meal. As you read and study this material, think about your own diet and assess whether you are meeting the requirements for nutri- ents that your body needs. Pages 488–489 discuss type 2 diabetes and cardiovascular disease, disorders that are asso- ciated with obesity. Carefully consider the MyPlate food guidelines in light of your own diet.

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Self-Check 25 1. The body mass index (BMI) is the ratio between a person’s height and

a. energy intake. c. age.

b. weight. d. energy output.

2. A deficiency of vitamin D can lead to bone decalcification and a disorder called

a. scurvy. c. rickets.

b. beriberi. d. pellagra.

3. Triglycerides are a form of

a. proteins. c. carbohydrate.

b. cholesterol. d. lipids.

4. If the body can’t produce a certain nutrient, it must be supplied by diet. Such a nutrient is

called

a. essential. c. healthful.

b. a macronutrient. d. a micronutrient.

5. Which one of the following vitamins is essential for strong bones and teeth?

a. Thiamine c. Riboflavin

b. Vitamin D d. Vitamin E

6. Which of the following is an example of a trace mineral?

a. Sodium c. Iodine

b. Phosphorus d. Calcium

Check your answers with those on page 198.

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ASSIGNMENT 26: DEFENSES AGAINST DISEASE Refer to the following information as you read Chapter 26 in your textbook.

The human body is continuously exposed to pathogens such as viruses and bacteria. Fortunately, vertebrate systems have developed various organic features that sustain the body’s immune system, which helps the body repel foreign substances, cancers, and pathogens. Immunity refers to the ability of the body to protect and defend itself against foreign substances.

Overview of the Immune System The organs of the immune system are called lymphatic organs, illustrated in Figure 26.1 on page 497. The lymphatic organs include red bone marrow, the thymus gland, lymph nodes, and the spleen, which are described on pages 497–499.

n Red bone marrow produces all kinds of blood cells, includ- ing cells important to the immune system. B lymphocytes (B cells) provide an antibody response to a pathogen. T lymphocytes (T cells) destroy antigen-bearing cells. Table 26.1 on page 498 lists and describes the types and function(s) of some of the immune cells that are pro- duced within red bone marrow.

n The thymus gland is where T cells mature. It produces thymic hormones that are believed to aid the maturing of T cells. Note that T cells have to pass a test before they’re released into the bloodstream; they must not react with or attack the body’s own cells—only poten- tially harmful foreign cells.

n The lymph nodes filter lymph of impurities such as pathogens and antigens. Sinuses (open spaces) in the lymph nodes are lined with macrophages, large cells that can engulf and consume as many as 100 pathogens.

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n The spleen, which is about the size of a fist, is where aging red blood cells go to be “recycled.” The spongy tissue of this organ is also adapted to filtering out all kinds of impurities from the blood, including debris and pathogens.

n The tonsils and the appendix are also areas of lymphatic tissue that contribute to immune system function.

Nonspecific Defenses and Innate Immunity The human body has four strategies for nonspecific defense against disease:

1. The skin and mucous membranes serve as body surface barriers to entry. Generally, pathogens can’t get past the linings of these surfaces. Figure 26.2 on page 499 illus- trates a cross section of human skin. Note that the outer cells of the dermis form the pathogen barrier.

2. The inflammatory response kicks in when a pathogen invades body tissues. Three kinds of white blood cells react swiftly to any tissue injury. Neutrophils, the most abundant type, ingest, kill, and digest bacterial cells. Mast cells release neutralizing chemicals, like histamine, which cause capillaries to dilate. This dilation causes the red- ness and swelling around a cut or abrasion. Macrophages also participate in the inflammatory response, releasing hordes of leukocytes into an affected area. Figure 26.3 on page 500 illustrates the inflammatory response.

3. The complement system is made up of a number of blood plasma proteins that complement certain kinds of immune response actions. Figure 26.4b on page 501 shows how plasma proteins combine to create a mem- brane attack complex that makes holes in the surface of a pathogen.

4. Natural killer cells (NK cells) are large granular lympho- cytes that kill cancer cells and cells infected by viruses in a manner similar to cytotoxic T cells. Figure 26.8 on page 505 illustrates the actions of cytotoxic T cells.

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Specific Defenses and Acquired Immunity Specific defenses require the presence of an antigen—a mole- cule that’s alien to the body and stimulates the immune system. Here’s a quick overview of specific immunity mecha- nisms, which are described in greater depth on pages 502–505.

B cells and T cells of the immune system have four outstand- ing features:

1. They ignore the body’s own cells.

2. Only a specific antigen triggers a B cell or T cell response.

3. The capacity of B cells and T cells to form receptors specific to particular antigens is enormous. Many mil- lions of specific antigen threats can be recognized and neutralized.

4. B cells and T cells have a biochemical memory. That is, after a cell responds to an antigen, a portion of the cell is set aside for future battles with the same pathogen.

To better understand the functions of B cells and T cells, study Figures 26.5 and 26.7, as well as Tables 26.2 and 26.4, on pages 502–504. Then study Figure 26.8 on page 505 to review the ways helper (cytotoxic) T cells regulate immunity by secreting cytokines.

Immunizations Make sure you understand the difference between passive and active immunity as described on pages 506–507. Passive immunity is temporary in that antibodies aren’t produced in the body but may be received through other means. For example, a newborn infant has passive immunity from the mother’s antibodies that crossed the placenta. Vaccines are used to induce an immune system response to a particular pathogen. In response to vaccine, active immunity is a meas- urable response in terms of antibody production largely by memory B cells.

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Immune System Problems The immune system typically protects us from infection; how- ever, in some cases it doesn’t work as it should. For example, allergies are specific responses to particular antigens (for example, plant pollens) that are identified as allergens. The body responds as though these antigens were disease organ- isms instead of environmental substances.

Severe autoimmune disorders, including myasthenia gravis and lupus, are examples of malfunctioning immune systems that attack the body’s tissues.

AIDS results from an infection with the HIV retrovirus, as graphed in Figure 26.12. Full-blown AIDS amounts to a gen- eral assault on the body’s immune system—making the body vulnerable to a wide range of pathogens and cancers.

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Self-Check 26 1. _______ T cells regulate immunity by secreting signaling chemicals called cytokines.

a. Receptor c. Granzyme

b. Helper d. Cytotoxic

2. A/An _______ is a molecule that stimulates the immune system.

a. antigen c. histamine

b. complement d. antibody

3. Which blood type contains plasma antibodies that are both anti-A and anti-B?

a. A c. AB

b. B d. O

4. In the inflammatory response, _______ release chemical mediators that cause capillaries to

dilate and become more permeable.

a. macrophages c. mast cells

b. killer NK cells d. neutrophils

5. T lymphocytes mature in the

a. red bone marrow. c. lymph nodes.

b. spleen. d. thymus gland.

Check your answers with those on page 199.

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ASSIGNMENT 27: THE CONTROL SYSTEMS Refer to the following information as you read Chapter 27 in your textbook.

Nervous Systems The central nervous system (CNS) of vertebrates, including humans, is composed of the brain and the spinal cord. The peripheral nervous system (PNS), which consists of cable-like bundles called nerves, carries signals from the brain and spinal cord to the rest of the body. Figure 27.1 on page 514 illustrates the ways in which the nervous and endocrine sys- tems work together. Figure 27.2 on page 515 compares the nervous systems in earthworms, planarians, and humans.

Neurons

Neurons, or nerve cells, respond to changes in voltages across their plasma membranes. The cell body and slender exten- sions called dendrites are the input zones for incoming signals. The signals, or nerve impulses, flow to the axon, a longer extension that serves as a conducting zone. Axon endings are the output zones for signals to be sent on to the dendrites of other cells. Long axons are protected by a myelin sheath that’s composed of tightly coiled cells. Occasional gaps in the sheath are called nodes of Ranvier.

The three different types of neurons found within the nervous system, sensory neurons, interneurons, and motor neurons, are described on page 516 and pictured in Figure 27.3.

The Nerve Impulse

When neurons are triggered by an abrupt change in voltage called an action potential (the nerve impulse), they conduct a signal through their axons. At the axon terminal, the signal is passed to the next neuron by way of molecules called neurotransmitters. Study the figures on pages 517–518 to

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understand how this process works. Myelinated axons use salutatory conduction, which allows signal transmission to proceed much quicker than in unmyelinated axons.

The Synapse

The synapse is the zone where the terminal of one neuron meets the dendrites of another. Neurotransmitters diffuse across the synaptic cleft, a narrow space between a neuron’s output zone and the input zone of a neighboring cell. This system allows messages traveling through the nervous sys- tem to either be reinforced or suppressed, depending on the intensity of the signal. Figure 27.6 will help you distinguish the synapse from the synaptic cleft and visualize the way neurotransmitters travel across that cleft.

The Central Nervous System

As already mentioned, the CNS consists of the brain and the spinal cord. The brain is the master control system of the body. It receives, integrates, stores, and retrieves sensory information. The brain is protected by the cranium as well as by fluid-filled protective membranes. In effect, the surround- ing fluids cushion brain tissues. The spinal cord is the expressway for signals between the brain and the peripheral nervous system. Signals travel swiftly up and down the cord. The spinal cord is also responsible for reflexes, involuntary protective reactions like pulling a hand away from a flame.

The brain includes the following functional divisions, as illus- trated in Figure 27.8 and described on pages 520–522:

n The cerebrum, the largest part of the brain, is divided into two halves, each of which has a number of divisions called lobes. The convoluted outer layer of the cerebrum, called the cerebral cortex, manages responses to sensa- tions, voluntary movement, and higher thought processes such as reasoning. Each lobe in the cerebrum has spe- cialized functions, as shown in Figure 27.9 on page 521.

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n The diencephalon lies beneath the cerebrum. In the diencephalon are the hypothalamus, which helps main- tain homeostasis, and the thalamus, which receives sensory information and sends it to the appropriate area of the cerebrum.

n The cerebellum receives and processes information from the various senses, both external and internal. It then fine-tunes motor responses. For example, since the cere- bellum in cats is highly developed, their movements are graceful and fluid.

n The brain stem contains the midbrain, the pons, and the medulla oblongata. The medulla oblongata contains reflex centers for managing heartbeat, breathing, and blood pressure. It’s also responsible for reflexes like sneezing, coughing, swallowing, and vomiting.

The limbic system can be thought of as a cooperative complex involving different parts of the CNS, including the cerebrum and the diencephalon. The limbic system blends higher cog- nitive thought functions with basic human emotions like fear and pleasure. In the limbic system, the hippocampus acts to create associations between sensory experiences and memo- ries. Hearing the song that was playing when you were on your first date, for example, can evoke certain memories. This reaction is controlled by the hippocampus. Another part of the limbic system is the amygdala, an almond-like structure under the cerebrum. The amygdala is especially implicated in giving remembered experiences emotional, fearful, exciting, or arousing overtones. Figure 27.10 on page 522 shows the location of the thalamus, hippocampus, hypothalamus, and amygdala.

The Peripheral Nervous System

The PNS, introduced on page 523, consists of two subdivisions:

1. The somatic system carries signals about moving the head, trunk, and limbs. First, its sensory axons deliver information from receptors in the skin, skeletal muscles, and tendons to the central nervous system. Then, its motor axons deliver the commands from the brain and

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spinal cord to the skeletal muscles. This system controls the reflexes, or involuntary responses to stimuli, as pic- tured in Figure 27.12.

2. The autonomic system carries signals to and from smooth muscle, cardiac muscle, and glands. Figure 27.13 on page 525 illustrates the two divisions of the autonomic system: the parasympathetic division and the sympathetic division. Think of the parasympathetic sys- tem as associated with happy feelings and the sympathetic system as related to stress and perceived threats.

Endocrine System All animals use chemical messengers known as hormones, which are released into the bloodstream by endocrine glands. These hormones are carried to other parts of the body where they act on target cells to alter their activities. Collectively, the body’s sources of hormones make up the endocrine system. The organs of the endocrine system are illustrated in Figure 27.14 on page 526.

The Action of Hormones

There are two main categories of hormones:

1. Steroid hormones, which are soluble in lipids, can diffuse across the lipid bilayer of a cell membrane. Once inside the cell, they move into the nucleus, where they bind with a receptor. This complex then interacts with the cell’s DNA to call for the production of enzymes and other proteins to carry out a response to the hormonal signal. Steroid hormones are secreted by the adrenal glands and the gonads. Testosterone and estrogen are examples.

2. Peptide hormones are soluble in water. When they bind to receptors at the cell membrane, specific enzyme sys- tems become activated and lead to a cellular response; the hormone itself doesn’t enter the cell. Examples of peptide hormones include peptides, proteins, glyco – proteins, and modified amino acids.

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Review Figure 27.15 on page 527 to compare cell interactions between steroid and peptide hormones.

Hypothalamus and Pituitary Gland

Two major components of the endocrine system are the hypothalamus and the pituitary gland. Figure 27.16 on page 528 illustrates how the hypothalamus and the anterior lobe of the pituitary gland interact with the thyroid gland, the adrenal cortex, and the gonads. Note the great variety of bodily functions related to hormones produced and/or regu- lated by these powerhouse glands of the endocrine system.

Other Endocrine Glands

The thyroid, parathyroid, and adrenal glands, and the pan- creas, are all part of the endocrine system. Their functions and possible dysfunctions are provided on pages 529–532.

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Self-Check 27 1. Two important functions of the _______ system are learning and memory.

a. somatic c. cerebellum

b. limbic d. medulla

2. Signals are carried across a synaptic cleft by

a. neurotransmitters. c. dendrites.

b. neurons. d. axons.

3. Which of the following hormones is produced by the anterior pituitary gland and doesn’t affect

other endocrine glands?

a. Thyroid hormone c. Prolactin

b. Oxytocin d. Antidiuretic hormone

4. Which one of the following elements is part of the peripheral nervous system?

a. Brain stem c. Spinal cord

b. Ganglia d. Cerebellum

5. In the central nervous system, the hypothalamus and the thalamus are located in the

a. diencephalon. c. cerebellum.

b. cerebrum. d. primary motor area.

Check your answers with those on page 199.

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ASSIGNMENT 28: SENSORY INPUT AND MOTOR OUTPUT Refer to the following information as you read Chapter 28 in your textbook.

The Senses The inputs of the senses are correlated with motor outputs enacted by bodily movements associated with muscles. Figure 28.1 on page 537 illustrates the basic scheme of sensory inputs and motor outputs.

Chemical Senses

In the chemical senses, chemoreceptors detect chemical energy. For example, taste buds, found on the tongue, are stimulated by food molecules. As that happens, we experience different tastes, such as sweet, sour, bitter, and salty. The many com- binations of these four tastes account for the variety of tastes we can detect. In addition, chemoreceptors for the sense of smell detect odors from very tiny proportions of odor-produc- ing molecules in the air, such as those offered by a rose or a skunk. Figure 28.2 on page 538 illustrates chemoreceptors within the animal kingdom.

Hearing and Balance

Most vertebrates have a sense of hearing that involves structures that collect and amplify sound waves from the environment. Vertebrate ears also function in the sense of balance. Figure 28.5 on page 541 illustrates rotational equilibrium, related to the rotation of the head, and gravitational equilibrium, related to the tilting of the head.

The human ear is divided into three parts as shown in Figure 28.3 on page 539:

1. The outer ear collects sound waves from the environment through skin-covered flaps of cartilage called the pinna. The outer ear sends these waves to the middle ear.

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