Unit 3 Review 𖦹⋆｡°✩

Question 1

A researcher proposes a model of an enzyme-catalyzed reaction in which a reactant is converted to a product. The model is based on the idea that the reactant passes through a transition state within the enzyme-substrate complex before the reactant is converted to the product. Which of the following statements best helps explain how the enzyme speeds up the reaction?

Answer 1

A. The enzyme’s active site binds to and stabilizes the reactant, which decreases the free-energy change of the reaction.

B. The enzyme’s active site binds to and stabilizes the transition state, which decreases the activation energy of the reaction.

C. The enzyme’s active site binds to and stabilizes the product, which increases the amount of energy released by the reaction.

D. The enzyme’s active site binds to and stabilizes both the reactant and the product at the same time, which increases the reaction’s equilibrium constant.

Question 2

✩CORRECT ANSWER FOR 3.1, 1✩

Answer 2

B

Question 3

Which of the following statements best helps explain the reaction specificity of an enzyme?

Answer 3

A. The free energy of the reactants is greater than the free energy of the products.

B. The equilibrium constant of the reaction is much greater than 1.

C. The shape and charge of the substrates are compatible with the active site of the enzyme.

D. The concentration of the enzyme inside living cells is greater than the concentration of substrate.

Question 4

✩CORRECT ANSWER FOR 3.1, 2✩

Answer 4

C

Question 5

The enzyme hexokinase catalyzes the conversion of glucose to glucose-6-phosphate, which is an important step in glycolysis. The reaction involves the transfer of a phosphate group from ATP to glucose. Either a glucose molecule or a water molecule can fit in the active site of hexokinase. The presence of a water molecule in hexokinase’s active site would result in the hydrolysis of ATP to ADP instead of the conversion of glucose to glucose-6-phosphate. Which of the following statements best helps explain the reaction specificity of hexokinase?

Answer 5

A. Both glucose and water are polar molecules that form favorable interactions with charged and polar amino acid side chains in hexokinase’s active site.

B. Both glucose and water have oxygen atoms that can form covalent bonds with the phosphorus atoms of phosphate groups.

C. Glucose is an energy-rich organic molecule that can be broken down by glycolysis to produce ATP, whereas water is an inorganic molecule.

D. Glucose has the right shape and charge to cause hexokinase to undergo a structural change needed for catalysis, whereas water does not.

Question 6

✩CORRECT ANSWER FOR 3.1, 3✩

Answer 6

D

Question 7

Alcohol dehydrogenase (ADH) is an enzyme that aids in the decomposition of ethyl alcohol (C2H5OH) into nontoxic substances. Methyl alcohol acts as a competitive inhibitor of ethyl alcohol by competing for the same active site on ADH. When attached to ADH, methyl alcohol is converted to formaldehyde, which is toxic in the body. Which of the following statements best predicts the effect of increasing the concentration of substrate (ethyl alcohol), while keeping the concentration of the inhibitor (methyl alcohol) constant?༻

Answer 7

A. There will be an increase in formaldehyde because
activity increases.

B. Competitive inhibition will be terminated because ethyl alcohol will bind to methyl alcohol and decrease
activity.

C. The peptide bonds in the active site of the enzyme will be denatured, inhibiting the enzyme.

D. Competitive inhibition will decrease because the proportion of the active sites occupied by substrate will increase.

Question 8

Amylase is a protein that catalyzes the conversion of starch to simple sugars. Amylase activity in an aqueous solution can be measured by using iodine as a starch indicator. A solution containing iodine and starch will have a dark-blue color, whereas a solution containing iodine but no starch will have a light-brown color. The color change of an iodine solution from dark blue to light brown can be used to measure the rate at which starch is converted to simple sugars. A student designs an experiment to investigate the effect of environmental pH on amylase function. The design of the experiment is presented in Table 1. Which of the following statements best justifies the inclusion of test tube V as a control in the experiment?

Answer 8

A. It will provide a measurement of amylase activity at an acidic pH.

B. It will provide a measurement of amylase activity at a basic pH.

C. It will show the color change that occurs in the absence of enzyme activity.

D. It will show the color change that occurs in the absence of the amylase protein.

Question 9

✩CORRECT ANSWER FOR 3.2, 1✩

Answer 9

C

Question 10

A researcher claims that some bacteria contain factors that influence the function of a particular enzyme but other bacteria do not. To test the claim experimentally, the researcher will grow two different bacterial strains in separate liquid cultures and isolate the contents of the cells in each culture. The researcher will add different combinations of cellular contents, substrate, and enzyme to test tubes containing a buffer solution adjusted to the optimal pH of the enzyme and then measure the rate of product formation. The design of the researcher’s experiment is presented in Table 1. Which of the following statements best justifies the inclusion of test tubes 3 and 7 in the experiment?

Answer 10

A. They will show whether the isolated cellular contents have enzymatic activity.

B. They will show whether environmental pH
affects the function of the enzyme.

C. They will show the rate of product formation in the absence of bacterial factors.

D. They will show the rate of product formation in the absence of the substrate.

Question 11

✩CORRECT ANSWER FOR 3.2, 2✩

Answer 11

A

Question 12

A researcher designs an experiment to investigate the effect of environmental temperature on the function of an enzyme. For each trial included in the experiment, the researcher will add the enzyme and its substrate to an aqueous buffer solution and then measure the amount of product formed over 20 minutes. Which of the following must remain the same for all trials of this experiment?

Answer 12

A. The initial concentration of the substrate

B. The final concentration of the product

C. The three-dimensional structure of the enzyme

D. The temperature of the aqueous buffer solution

Question 13

✩CORRECT ANSWER FOR 3.2, 3✩

Answer 13

A

Question 14

Gelatin is a protein that is derived from collagen which is found in the bones, skin, and connective tissue of animals. To investigate the ability of various enzymes to digest gelatin, a group of students set up an assay involving camera film. Camera film contains gelatin and appears black when exposed to light but turns clear as the gelatin gets broken down. The students incubated pieces of exposed camera film in test tubes, each containing one of three different enzyme solutions (trypsin, lipase, or amylase) as indicated in Figure 1. The students recorded the time it took for the enzymes to digest the gelatin in each test tube, turning the film from black to clear. Which of the following would be the most appropriate control for this experiment?

Answer 14

A. A test tube containing no camera film

B. A test tube containing only a piece of exposed camera film

C. A test tube containing a piece of exposed camera film submerged in water

D. A test tube containing a piece of exposed camera film and all three enzyme solutions

Question 15

✩CORRECT ANSWER FOR 3.2, 4✩

Answer 15

C

Question 16

A researcher claims that different enzymes exhibit maximal function over different pH ranges. To test the claim, the researcher carries out an experiment that includes three different enzymes: pepsin, salivary amylase, and arginase. The results of the experiment are represented in Figure 1. Which of the following actions will provide the most appropriate negative control for the experiment?

Answer 16

A. Repeating the experiment with a fourth enzyme

B. Repeating the experiment at several different temperatures

C. Repeating the experiment with denatured enzymes

D. Repeating the experiment using several different methods for measuring pH

Question 17

✩CORRECT ANSWER FOR 3.2, 5✩

Answer 17

C

Question 18

A researcher claims that increasing the environmental temperature by 10C will double the rate of an enzyme-catalyzed reaction. To test the claim, the researcher designs an experiment that uses a particular enzyme isolated from plants. The design of the experiment is presented in Table 1. For each test tube in the experiment, the researcher will measure the rate of product formation. Which of the following statements best helps justify the inclusion of test tube 5 as a control in the experiment?

Answer 18

A. It will provide a measurement of product formation in the absence of the substrate.

B. It will provide a measurement of product formation in the presence of a denatured enzyme.

C. It will show the effect of doubling the amount of substrate on the rate of product formation.

D. It will show the effect of increased enzyme activity on the rate of product formation.

Question 19

✩CORRECT ANSWER FOR 3.2, 6✩

Answer 19

B

Question 20

✩CORRECT ANSWER FOR 3.3, 1✩

Answer 20

D

Question 21

The enzyme peroxidase is found in many organisms. It catalyzes the breakdown of hydrogen peroxide into water and oxygen gas. The rate of peroxidase activity at different pH values was assessed by students in the lab. The students’ results are shown in graph 1. If the experiment is repeated at pH 11, the observed activity level of the enzyme will most likely be

Answer 21

A. the same as the level at pH 7

B. lower than the level at pH 9

C. greater than the level at pH 9

D. between the levels observed at pH 5 and pH 7.

Question 22

✩CORRECT ANSWER FOR 3.3, 2✩

Answer 22

B

Question 23

Protein digestion in humans is primarily carried out by three enzymes. Pepsin is found in the stomach (pH 2), where it aids in the breakdown of large proteins into smaller peptides, while trypsin and chymotrypsin are found in the small intestine (pH 8), where they aid in the further breakdown of the proteins into amino acids and dipeptides that can be absorbed into the bloodstream. Graph 1 shows the effect of pH on the activity levels of the three enzymes. Which of the following best predicts how the structure and function of pepsin will change as it enters the small intestine?

Answer 23

A. Pepsin will not change in shape and will continue to break down proteins in the small intestine.

B. Pepsin will not change in shape but may not work due to the basic environment of the small intestine.

C. Pepsin will change in shape because of the basic environment of the small intestine; therefore, its enzymatic activity will decrease.

D. Pepsin will change in shape because of the presence of trypsin and chymotrypsin in the small intestine, both of which act as competitive inhibitors.

Question 24

✩CORRECT ANSWER FOR 3.3, 3✩

Answer 24

C

Question 25

A researcher claims that the synthesis of ATP from ADP and inorganic phosphate (Pi) is essential to cellular function. Which of the following statements best helps justify the researcher’s claim?

Answer 25

A. ADP is a small molecule that some cells release into their environment as a way of communicating with other cells.

B. ADP hydrolysis is an energy-releasing reaction that is often coupled with reactions that require an input of energy.

C. Inorganic phosphate is a substance that cells typically acquire from their environment.

D. ATP synthase is a mitochondrial enzyme that catalyzes the conversion of ADP
and Pi to ATP.

Question 26

✩CORRECT ANSWER FOR 3.4, 1✩

Answer 26

B

Question 27

A researcher claims that only a portion of the light energy captured by green plants is available for growth and repair. Which of the following observations best helps justify the researcher’s claim?

Answer 27

A. Light-capturing pigment molecules in green plants absorb red, blue, and violet light but reflect green light.

B. The energy of a photon of light is proportional to its frequency and inversely proportional to its wavelength.

C. As light energy is converted to chemical energy by metabolic processes, some of the energy is lost as heat.

D. Captured energy is stored in the molecular bonds of organic molecules, including simple sugars and starch.

Question 28

✩CORRECT ANSWER FOR 3.4, 2✩

Answer 28

C

Question 29

Muscle contraction depends on ATP hydrolysis. During periods of intense exercise, muscle cells rely on the ATP supplied by three metabolic pathways: glycolysis, mitochondrial respiration, and the phosphagen system. Figure 1 shows the rates at which the three metabolic pathways produce ATP following the start of an intense period of exercise. Which of the following correctly uses the data to justify the claim that the phosphagen system is an immediate, short-term source of ATP for muscle cells?

Answer 29

A. ATP production by the phosphagen system increases and decreases rapidly following the start of the exercise period.

B. ATP production by the phosphagen system increases gradually and continuously throughout the entire exercise period.

C. The ATP produced by the phosphagen system contains more energy per molecule than does the ATP produced by the other pathways.

D. ATP hydrolysis in muscle cells occurs immediately after the start of the exercise period but stops before the end of the exercise period.

Question 30

✩CORRECT ANSWER FOR 3.4, 3✩

Answer 30

A

Question 31

A researcher claims that increased atmospheric carbon dioxide levels cause increased growth rates in plants. Which of the following statements best supports the researcher’s claim?

Answer 31

A. Atmospheric carbon dioxide is produced by the burning of fossil fuels, which are formed from the remains of living organisms such as plants.

B. Atmospheric carbon dioxide is a byproduct of cellular respiration, which is a metabolic process that occurs in plants and other living organisms.

C. Atmospheric carbon dioxide typically enters plant leaves through stomata, which plants rely on for regulating gas exchange with the atmosphere.

D. Atmospheric carbon dioxide is the raw material for photosynthesis, which plants rely on for producing sugars and other organic compounds.

Question 32

✩CORRECT ANSWER FOR 3.5, 1✩

Answer 32

D

Question 33

In chloroplasts, ATP is synthesized from ADP plus inorganic phosphate (Pi) in a reaction catalyzed by ATP synthase molecules that are embedded in the thylakoid membrane. Which of the following statements provides evidence to support the claim that no ATP will be synthesized in the absence of a proton gradient across the thylakoid membrane?

Answer 33

A. Blocking electron flow from one carrier to the next in the electron transport chains blocks formation of a proton gradient in the thylakoid.

B. Increasing the proton concentration difference across the thylakoid membrane is not associated with a parallel increase in the rate of ATP synthesis.

C. No ATP is synthesized when channel proteins that allow the free passage of protons are inserted into the thylakoid membrane.

D. No ATP is synthesized while the Calvin cycle is synthesizing carbohydrates and using ATP and NADPH at a high rate.

Question 34

✩CORRECT ANSWER FOR 3.5, 2✩

Answer 34

C

Question 35

✩CORRECT ANSWER FOR 3.5, 3✩
… short answer question

Question 36

✩CORRECT ANSWER FOR 3.5, 4✩
… short answer question

Question 37

A scientist claims that Elysia chlorotica, a species of sea slug, is capable of photosynthesis. Which of the following observations provides the best evidence to support the claim?

Answer 37

A. Elysia chlorotica will die if not exposed to light.

B. Elysia chlorotica grows when exposed to light in the absence of other food sources.

C. Elysia chlorotica grows faster when exposed to light than when placed in the dark.

D. Elysia chlorotica grows in the dark when food sources are available.

Question 38

✩CORRECT ANSWER FOR 3.5, 5✩

Answer 38

B

Question 39

A researcher claims that different metabolic pathways allow bacteria to use different molecules as sources of matter and energy. Which of the following statements best helps justify the researcher’s claim by providing a relevant example?

Answer 39

A. Rhizobia bacteria form close associations with the roots of bean plants.

B. E. coli bacteria reproduce in liquid media containing either glucose or galactose.

C. The antibiotic rifampicin inhibits the growth of some bacterial strains but not of others.

D. Some viruses that infect bacteria reproduce by either the lysogenic cycle or the lytic cycle.

Question 40

✩CORRECT ANSWER FOR 3.7, 1✩

Answer 40

B

Question 41

Cyanobacteria contain a variety of pigment molecules, as shown in Table 1. As a result, the color of cyanobacteria cultures can vary significantly based on the relative amount of each pigment produced. A researcher placed a culture of cyanobacteria under green lights. Within a few weeks, the appearance of the cyanobacteria changed from green to red. The researcher claimed the color change in the culture was the result of an adaptation allowing greater photosynthesis. Which of the following provides the best reasoning to justify the researcher’s claim?

Answer 41

A. In green light, more chlorophyll a molecules are produced, reflecting more light to other cyanobacteria to be used for photosynthesis.

B. In green light, more phycoerythrin molecules are produced, allowing more green light to be absorbed, thus increasing photosynthesis.

C. In green light, cyanobacteria that have more phycocyanin molecules are less likely to survive and reproduce.

D. In green light, cyanobacteria that have more allophycocyanin molecules are more likely to survive and reproduce.

Question 42

✩CORRECT ANSWER FOR 3.7, 2✩

Answer 42

B

Question 43

In addition to the pigments commonly associated with photosynthesis, a certain photosynthetic species contains two additional pigment types. Which of the following best supports the claim that this species is better adapted to environmental changes than other photosynthetic species are?

Answer 43

A. The increased pigment concentration better facilitates energy production within the cells of the species.

B. The pigment combination allows the organism to absorb heat as well as light, making better use of available energy.

C. The additional pigments allow the species to outcompete other species for the wavelengths of light commonly used in photosynthesis.

D. The additional pigments allow the species containing them to harvest energy from wavelengths of light that the other photosynthetic species cannot use.

Question 44

✩CORRECT ANSWER FOR 3.7, 3✩

Answer 44

D