BIOLOGY 2.

Directions

Accurately measuring the volume of liquids, weighing chemicals, and adjusting the pH of solutions are routine procedures in a working laboratory environment. This assignment is designed to provide you with an overview of the general skills and knowledge you would need to perform such tasks.

Before completing this assignment, you should ensure you have read your textbook – particularly the section entitled pH, Buffers, Acids, and Bases. Answers should be concise and well written. Make sure you correctly explain your thought process and provide all the necessary information.

 

Question 1 

The pH of a solution describes its acidity or alkalinity: Describe how pH and H3O+ concentration are related and explain why diluting an acid raises the pH, but diluting a base lowers the pH.

 

Question 2

Phosphate Buffered Saline (PBS) is a commonly used buffer for experiments in biology because its pH and ion concentrations are similar to those in mammalian organisms. It works in a similar fashion to the blood plasma buffer mentioned in the textbook, but using dihydrogen phosphate ions and hydrogen phosphate ions for buffering through the following chemical reaction:

H2PO4- (aq)  ⇆  H+(aq) + HPO42–(aq)

 

The equilibrium arrows depict that the phosphate ion (H2PO4- ) is dissociating further into two component ions in solution, but at the same time H+ and HPO42- ions are combining simultaneously to form phosphate in solution. So, at any given point in time, and under the appropriate conditions, there is an equal quantity of dissolved ions and combined ions in solution. There is therefore always a hydrogen ion donor and an acceptor in solution.

 

Based on the equation above, which ion plays the role of hydrogen-ion donor (acid) and which ion plays the role of hydrogen-ion acceptor (base) in PBS?

 

Question 3

 

The composition of PBS is 0.137M NaCl, 0.012M Phosphate, 0.0027M KCl, pH 7.4. Below is the protocol to make 1 litre of 10x concentrate PBS.

Combine the following:

· 80g NaCl

· 2g KCl

· 14.4g Na2HPO4 (dibasic anhydrous)

· 2.4g KH2PO4 (monobasic anhydrous)

· 800mL distilled H2O

1. Adjust pH to 7.4 with HCl

2. Add H2O to 1L

3. Autoclave for 20 minutes on liquid cycle. Store at room temperature.

Which ions are being produced by this process, assuming that each of the chemical compounds dissociate into their constituent parts once they are dissolved in water?

Question 4

Preparation of the correct buffer is key to any good biological experiment and it is important that you understand how to calculate the mass of each chemical required to make that buffer and what the resulting concentration of those constituents will be in moles per litre.

Your text book explains that moles are just a way to express the amount of a substance, such that one mole is equal to 6.02 x 1023 particles of that substance. These particles can be can be atoms, molecules, ions etc, so 1 mole of water is equal to 6.02 x 1023 water molecules, or 1 mole of Na+ is equal to 6.02 x 1023  Na+ ions. Since different chemicals have different molecular weights (based on the number of protons and neutrons each atom contains) 1 mole or 6.02 x 1023 atoms of oxygen (O) will have a mass of 16g whereas 1 mole or 6.02 x 1023 atoms of sodium (Na) will have a mass of 23g

If you need more information on moles, please read Encyclopedia Britannica’s Moles website.

Although you may sometimes see it written as g/litre, the concentration of solutions is more often described in term of molarity since it better defines the chemical properties of a solution because it is proportional to the number of molecules or ions in solution, irrespective of molecular mass of its constituents. However, it is not possible to measure moles on a laboratory balance, so in the first instance chemicals are measured by mass (milligrams, grams, kilograms etc) and the number of moles is calculated using the known molecular mass (often called molecular weight and abbreviated to M.W.) of the chemical. As indicated earlier, the molecular mass of a chemical is based on the number of protons and neutrons that is contained in each atom (eg NaCl is made up of one molecule of Na, M.W. = 22.99g and one molecule of Cl, M.W. = 35.45g, so the M.W. of NaCl is 58.44g). These values can be found in the periodic table however the molecular mass of chemicals is generally provided by any vendors of the products and so can also be found on various suppliers’ websites.

 

When the concentrations of solutions are as described as ‘molar’, this refers to number of moles per litre eg a 3-molar solution of NaCl will contain 3 moles of NaCl in 1 litre of water. As indicated above, the M.W. of NaCl is 58.44g, so in 58.44g there are 6.02 x 1023 NaCl molecules ie 1 mole. So, for 3 moles of NaCl you would need to dissolve 175.32g in 1 litre of water (175.32/58.44 =3) whereas If you only dissolved 29.22g of NaCl in 1 litre of water this would result in a 0.5 molar solution (29.22/58.44= 0.5)

 

1. As directed you need to check the periodic table and pick up the atomic masses for each of the component atoms in the compounds. For example, for NaCl you need to pick the atomic weight of both sodium and chlorine and then add them to two decimal places to obtain the molecular mass of NaCl. Be sure to multiply the atomic masses by the number of individual atoms of the same element present in each compound before finally adding to the masses of other component atoms of other elements to make up the total molecular masses.

 

2. From there you can calculate the number of ‘moles’ of each compound by multiplying the provided weight of compound used in the PBS solution by their respective molar mass conversion factors (i.e. 1L divided by the molecular mass you have calculated in the first step)

 

3. Now, the molarity in Mol per Litre (mol/l) is given by the ‘number of moles’ of each compound (calculated in step 2 above) divided by the given volume of the solution.

For more information on how to calculate morality, refer to wikiHow’s 4 Ways to Calculate Molarity.

Using periodic table found in your textbook, calculate (to 2 decimal places) the molecular mass for each of the compounds used to make PBS.

Create the following table and fill it in with the mass of each component required to make 1 litre of 10 x PBS (the recipe for 10x PBS is below question 2) and their final molar concentration in the buffer calculated as described above.

 

Compound formula	Molecular mass (in g/mol)	Mass of compound per litre of 10x PBS (in g)	Molar concentration (in mol/l)
NaCl
KCl
Na2HPO4
KH2PO4

 

Question 5

As previously stated, the concentration of NaCl, KCl and Phosphate in working strength 1 x PBS is 0.137M NaCl, 0.012M Phosphate, 0.0027M KCl,  pH 7.4   How do they compare to the concentrations you calculated for 10x PBS?

 

Watch the following videos and answer the remaining questions

 “Using an Electronic Balance” from Bio-Rad tutorials

 “Using a pH Meter” from Bio-Rad tutorials

 “ Making a PBS solution ” from Community College Consortium for Bioscience Credentials

Question 6

What is the first thing to do after putting a weighing boat on the balance?

 

Question 7

If you have excess reagent on the weighing boat, what should you avoid doing and why?

 

Question 8

If you had the choice between a 1-litre beaker and a 1 litre graduated cylinder, which one should you use to measure volumes with maximal precision when making 1 litre of PBS? (you can perform an internet search to find this if you are not sure of the answer)

 

Question 9

What should be done before measuring an unknown pH of a solution using a pH meter?

 

Question 10

The recipe for PBS says to dissolve compounds in 800 ml of water, adjust the pH to 7.4, then add water up to 1 litre. The final pH should still be 7.4, because the pH of buffer solutions remains stable when they are diluted as long as the concentration of its constitutive acid and base is not too low.

 

Why do you think the protocol does not say to dissolve compounds directly in 1 litre of water?

 

Question 11

The PBS protocol above says to adjust pH to 7.4 with HCl. What does this imply on the pH of 10x PBS before adjusting the pH, would it be greater or smaller than 7.4?

 

Question 12

The last step in the protocol is to autoclave the 10x PBS solution. Why do you think this step is important? Look up the definition of autoclave if you are unsure what it means.

 

Question 13

Taking into account your response to question 5, now that you have made a 10x PBS solution, describe how you would prepare 1 litre of 1x working solution PBS, including which glassware you would use. Will you need to adjust the pH again?

 

www.UoPeople.edu

BIOLOGY 2

 

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Genetics Worksheet Gregor Mendel’s Experiments, Theories, and Findings. Unit II Assignment—Genetics Worksheet

 

 

Gregor Mendel’s Experiments, Theories, and Findings

 

1. Mendel observed that pea plants had traits, such as color, that were either “one or the other,” never something in between. In your own words, discuss the correlation between Mendel’s factors, what they might be, and why pea plant traits come in one form or another—e.g., gray or dark red—rather than blended.

 

Your response must be at least 75 words in length. (Type your response in the blank area below; it will expand as needed.)

 

 

2. Let’s imagine that we are studying only one trait, that of green- or yellow-colored seeds. Mendel bred his peas until they either produced seeds of one color or the other. These purebred plants he called the p generation (“p” for parental generation). He then cross bred green plants with yellow ones and discovered that all the offspring were yellow-colored. Mendel called the offspring of the purebred plants the F1 generation.

 

In your own words, explain why all the offspring in the F1 generation were yellow instead of half being yellow and half green, or some other mix of the colors. Hint: Remember that Mendel coined the terms dominant and recessive.

 

Your response must be at least 75 words in length. (Type your response in the blank area below; it will expand as needed.)

Punnett Squares Reginald Punnett was a British geneticist who developed the Punnett square to explain how the chromosomes of parents cross and produce offspring. In order to solve genetics problems using a Punnett square, it is necessary to a) understand the associated vocabulary and b) understand some of the rules for solving the problems.

 

· Before you continue with the problems below, review the meaning of the terms allele, dominant, recessive, homozygous, heterozygous, genotype and phenotype.

 

· You should also review the Punnett Square Basics video linked in the unit lesson.

 

In this first problem (question #3), the key and genotype of the parents will be done for you as an example. For problems #4 and #5, you will fill in those details based on the information in the question. Remember, when asked for the genotypic ratio, it may be expressed as 25%(GG):50%(Gg):25%(gg), for example. Or, you may write it more succinctly as 1GG:2Gg:1gg. Either way will be correct. The phenotypic ratio will use descriptive terms, for example, 3(Green):1(clear), 2(Green):2(clear), or whatever it may be depending on the results of your cross. 3. In corn plants, the allele for green kernels (G) is dominant over clear kernels (g). Cross a homozygous dominant plant with a homozygous recessive plant.

 

Fill in the Punnett square below and give the ratios for each question beneath the Punnett Square.

 

 

 

Key: G = green kernels, g = clear kernels Genotype of parents: _GG_ x _gg_

 

Parent #1
Parent #2

 

 

What is the genotypic ratio of the offspring in Question 3? What is the phenotypic ratio of the offspring in Question 3?

4. Yellow seeds are dominant over green seeds in pea plants. Cross a heterozygous (yellow seeded) plant with a green seeded plant.

 

Key: __________ Genotype of parents: __________ x __________

 

Parent #1
Parent #2

 

What is the genotypic ratio of the offspring in Question 4? What is the phenotypic ratio of the offspring in Question 4?

 

 

 

 

5. Now cross two of the heterozygous F1 offspring from question #2.

 

Parent #1
Parent #2

 

What is the genotypic ratio of the offspring in Question 5? What is the phenotypic ratio of the offspring in Question 5?

6. Consider the resulting ratio of crossing the two heterozygous pea plants in question #5. We will use this ratio in a short activity exploring probability. Keep in mind that crossing two individuals that are heterozygous for a certain trait is similar to flipping two coins. Each coin has two sides (we might think of each side as an “allele”) and the chances of flipping heads/heads, heads/tails or tails/tails should be similar to the ratio we see when crossing two heterozygotes. For this simple activity, you will need two coins (pennies, nickels, dimes, quarters, or a mix of any of those). Alternatively, you may google a coin-flipper simulator that will allow you to flip two coins at once. You will also need a piece of scratch paper and a pen or pencil. Directions: Flip the two coins simultaneously at least 50 times. For each flip of the pair of coins, you will record the results on a piece of scratch paper. You might set up a table like the one below to record your results. Once you have flipped the coins at least 50 times, enter the number of heads/heads, heads/tails and tails/tails in Table 1 below. Now determine the ratio for your results. You will do this by dividing the number for each result by the total number of flips, and then multiply by 100. (Example: If the number of heads/heads is 9 then 9/50 = .18, .18×100 = 18%), Repeat this mathematical procedure for heads/tails and tails/tails)

 

Table 1
Heads/heads (hh)
Head/tails (ht)
Tails/tails (tt)
Ratio (hh:ht:tt)

 

 

Compare the resulting ratio from the question #5 cross of two heterozygous parents to the ratio from the coin flipping exercise. Are there similarities? If so, what are they? What might be done to make the ratio from the coin flipping exercise become more similar to the ratio from question #5? (Hint: Consider that more data equals better accuracy.)

 

 

 

Cancer Risk Factors

 

6. This question deals with cancer and risk factors. Begin by going to the website http://www.cancer.org/

 

Click “Cancer A-Z” in the upper left corner. The page that comes up will provide links to information on breast cancer, colon and rectal cancer, lung cancer, prostate cancer, and skin cancer. Review the information for each these cancers.

 

Next, write an essay that discusses your own risk factors for each type of cancer and steps you might take to decrease those risk factors. Be sure to address all five types of cancer.

 

You do not have to disclose any actual personal information if you do not wish to do so. You may create a fictional character and discuss his or her risk factors instead. Be sure to address all five types of cancer.

 

Your response must be at least 300 words in length. (Type your response below)

 

 

 

 

 

Genetics Worksheet Gregor Mendel’s Experiments, Theories, and Findings

 

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