AP Biology Unit 3 Practice Test & Exam | 21 Questions

Questions 1-2 refer to the following graph, which shows the effect of pH on the reaction rate of two different enzymes, pepsin and trypsin.

1. Which of the following statements best describes the data presented in the graph?

(A)Both enzymes exhibit maximum activity under acidic conditions.(B)Pepsin has a higher maximum reaction rate than trypsin.(C)Each enzyme functions best within a specific, narrow pH range.(D)Enzyme activity is directly proportional to pH for both enzymes.

2. A student claims that if pepsin, which is found in the stomach, were moved to the small intestine (where the pH is approximately 8), it would continue to function. Which of the following best explains why this claim is incorrect?

(A)The high concentration of trypsin in the small intestine would competitively inhibit the pepsin.(B)The basic environment of the small intestine would cause the pepsin to denature, altering the shape of its active site.(C)The substrate for pepsin is only found in the stomach, so there would be nothing for it to catalyze in the small intestine.(D)The higher temperature of the small intestine would exceed the optimal temperature for pepsin activity.

3. Enzymes catalyze metabolic reactions by lowering the activation energy. Which of the following is a direct consequence of this function?

(A)The total energy released by the reaction increases.(B)The rate of the reaction increases significantly.(C)The reaction becomes endergonic instead of exergonic.(D)The equilibrium point of the reaction is shifted in favor of the products.

4. The induced-fit model of enzyme action describes the formation of an enzyme-substrate complex. Which of the following statements correctly describes this interaction?

(A)The enzyme is a rigid structure, and only substrates with a perfectly matching shape can bind to the active site.(B)The binding of the substrate to the active site is a permanent covalent bond that alters the enzyme.(C)The substrate binds to a random location on the enzyme, which then forms an active site around it.(D)The binding of the substrate induces a slight change in the shape of the enzyme's active site for a tighter fit.

Questions 5-7 refer to the following diagram of a mitochondrion.

5. Which letter indicates the location where the Krebs cycle and the oxidation of pyruvate occur?

(A)W(B)X(C)Y(D)Z

6. The structure labeled X is highly folded. How does this structural feature relate to the function of the mitochondrion?

(A)The folds decrease the volume of the matrix, concentrating the substrates for the Krebs cycle.(B)The folds increase the surface area available for the electron transport chain and ATP synthase proteins.(C)The folds allow for more efficient transport of pyruvate from the cytoplasm into the mitochondrion.(D)The folds create physical barriers that separate the different reactions of the Krebs cycle from each other.

7. During oxidative phosphorylation, a high concentration of protons ($H^+$) is established in the location labeled Y. What is the direct result of the flow of these protons through ATP synthase?

(A)$NAD^+$ is reduced to form $NADH$.(B)Oxygen is split to form water molecules.(C)ADP and $P_i$ are combined to form ATP.(D)Pyruvate is oxidized to form acetyl-CoA.

8. Living systems must maintain a state of order, or low entropy, which appears to contradict the second law of thermodynamics. Which of the following statements best explains how life is compatible with this law?

(A)Living systems create energy to counteract the increase in entropy.(B)Living systems are closed systems that are not subject to the second law of thermodynamics.(C)Living systems are open systems that use a constant input of energy to maintain order, while increasing the entropy of their surroundings.(D)The evolution of enzymes has allowed living systems to reverse the direction of entropy.

9. Glycolysis is a metabolic pathway that occurs in the cytoplasm of all known living organisms. Which of the following claims is best supported by this observation?

(A)Glycolysis produces more ATP than any other metabolic pathway.(B)Glycolysis is a key process in photosynthesis that evolved in plants.(C)The enzymes for glycolysis are only synthesized in the presence of oxygen.(D)Glycolysis is an ancient, conserved pathway, suggesting a common ancestor for all domains of life.

Questions 10-12 refer to an experiment designed to measure the rate of photosynthesis in spinach leaf discs.

10. Which of the following statements correctly describes a pattern in the data?

(A)The rate of photosynthesis is fastest under green light.(B)As the wavelength of light increases, the rate of photosynthesis consistently decreases.(C)The spinach leaf discs photosynthesize most efficiently in blue and red light.(D)White light is less effective for photosynthesis than any specific color of light.

11. Which of the following is the most likely reason for the results observed for the discs in green light?

(A)Green light has the highest energy per photon, which damages the chlorophyll pigments.(B)Chlorophyll and other accessory pigments do not absorb green light; they reflect it.(C)The sodium bicarbonate solution turns green in green light, blocking the light from reaching the discs.(D)The enzymes of the Calvin cycle are denatured by the specific wavelength of green light.

12. If a student were to graph the net rate of photosynthesis (proportional to $1/ET_{50}$) versus light color, which of the following graphs would best represent the expected results?

(A)A bar graph with the tallest bar for Green and the shortest bars for Blue and Red.(B)A bar graph with the tallest bars for Blue and Red and the shortest bar for Green.(C)A bar graph with bars of approximately equal height for all colors.(D)A bar graph with the tallest bar for White and progressively shorter bars for Blue, Green, and Red.

13. Which of the following correctly identifies the source of the oxygen produced during the light-dependent reactions of photosynthesis?

(A)The breakdown of carbon dioxide ($CO_2$) in the Calvin cycle.(B)The splitting of water molecules ($H_2O$) at photosystem II.(C)The reduction of $NADP^+$ to $NADPH$.(D)The synthesis of ATP by ATP synthase.

Questions 14-15 refer to the diagram below, which shows a process occurring on the thylakoid membrane.

14. Which of the following statements accurately describes a component of the process shown?

(A)The Calvin cycle occurs in the thylakoid space, where there is a high concentration of protons.(B)$NADP^+$ acts as the final electron acceptor, forming $NADPH$.(C)Carbon dioxide is the source of electrons for the electron transport chain.(D)ATP synthase pumps protons from the stroma into the thylakoid space.

15. The process shown is known as photophosphorylation. Which of the following statements best explains the relationship between the two stages of photosynthesis?

(A)The ATP and $NADPH$ produced in this process are used in the Calvin cycle to convert $CO_2$ into carbohydrates.(B)The glucose produced in the Calvin cycle is broken down on the thylakoid membrane to power this process.(C)This process releases oxygen, which is the final electron acceptor in the Calvin cycle.(D)The protons pumped during this process are directly incorporated into glucose molecules in the stroma.

16. Photosynthesis first evolved in prokaryotic organisms. Which of the following is the most likely consequence of the evolution of this process?

(A)A decrease in atmospheric carbon dioxide and an increase in atmospheric oxygen.(B)The evolution of glycolysis to break down the first organic molecules.(C)A global cooling event due to the absorption of solar radiation by chlorophyll.(D)The extinction of all anaerobic life forms.

17. In the absence of oxygen, some organisms can perform fermentation. The primary function of fermentation is to:

(A)produce a large amount of ATP through substrate-level phosphorylation.(B)generate oxygen so that aerobic respiration can resume.(C)regenerate $NAD^+$ from $NADH$ to allow glycolysis to continue.(D)break down pyruvate into carbon dioxide and water.

Questions 18-19 refer to the following experiment.

18. Based on the experimental results, which of the following statements best describes the mechanism of malonate?

(A)Malonate is a noncompetitive inhibitor that changes the shape of the electron transport chain proteins.(B)Malonate is a competitive inhibitor that binds to the active site of succinate dehydrogenase.(C)Malonate blocks the transport of pyruvate into the mitochondrial matrix.(D)Malonate prevents oxygen from acting as the final electron acceptor.

19. Which of the following best explains why oxygen consumption is high in Tube 2 but low in Tube 1?

(A)Mitochondria lack the enzymes required for glycolysis, the first step in breaking down glucose.(B)Glucose is too large a molecule to diffuse across the mitochondrial membranes.(C)Oxygen is only required for the Krebs cycle, which starts with pyruvate, not glucose.(D)The breakdown of glucose to pyruvate consumes oxygen, leaving less for the mitochondria.

AP Biology Unit 3: Cellular Energetics Practice Exam

Exam Details

A. Multiple-Choice Questions (19 Questions)

B. Short Answer Questions (2 Questions)

AP Biology Unit 3: Cellular Energetics Practice Exam

Exam Details

A. Multiple-Choice Questions (19 Questions)

B. Short Answer Questions (2 Questions)