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AP Biology Unit 3: Cellular Energetics

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Unit 3: Cellular Energetics

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Question 1

A scientist discovers a novel inhibitor that competes with NAD⁺ at the active site of isocitrate dehydrogenase in the Krebs cycle. If this inhibitor is added to a cell, which of the following best predicts the downstream effects?

A.NADH production increases and ATP yield per glucose risesB.Isocitrate accumulates, the Krebs cycle slows, and overall ATP yield from aerobic respiration decreasesC.The cell shifts entirely to glycolysis with no change in total ATP outputD.Pyruvate oxidation accelerates to compensate for reduced Krebs cycle activity

Question 2

A cell has a high ratio of AMP to ATP. This condition allosterically activates phosphofructokinase-1 (PFK-1), a key enzyme in glycolysis. Which of the following best explains why this regulation is adaptive?

A.It prevents overproduction of pyruvate when ATP is abundant, conserving glucoseB.It accelerates ATP production precisely when the cell's energy charge is low, restoring homeostasisC.It inhibits the Krebs cycle to prevent further energy expenditureD.It signals the cell to begin gluconeogenesis to produce more glucose from amino acids

Question 3

Which of the following is the direct product of glycolysis when one molecule of glucose is completely processed?

A.2 acetyl-CoA, 2 ATP, 2 NADHB.2 pyruvate, 2 ATP (net), 2 NADHC.4 pyruvate, 4 ATP, 4 NADHD.2 pyruvate, 36 ATP, 2 NADH

Question 4

A mutation eliminates the enzyme RuBisCO from a plant cell. Which stage of photosynthesis would be most directly affected?

A.The light-dependent reactions in the thylakoid membranesB.The splitting of water molecules (photolysis)C.Carbon fixation in the Calvin cycleD.ATP synthesis via the electron transport chain

Question 5

In a C₃ plant, the Calvin cycle consumes ATP and NADPH to fix CO₂. Under conditions of high light intensity but a sudden drop in CO₂ concentration (stomata close due to drought), which of the following would be expected?

A.RuBP levels decrease because the Calvin cycle continues to consume it at the same rateB.ATP and NADPH accumulate while RuBP builds up, and photorespiration may increaseC.The light reactions slow down because there is less demand for ATP and NADPHD.Glucose production increases because the Calvin cycle is no longer limited by light

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Question 6

An enzyme lowers the activation energy of a reaction. Which of the following best describes how the enzyme accomplishes this?

A.By adding energy to the reactants to push the reaction forwardB.By stabilizing the transition state, reducing the energy required to reach itC.By permanently bonding to the substrate and forming a new productD.By increasing the temperature of the reaction environment

Question 7

A particular organism lives in an environment with abundant light and CO₂ but very little inorganic phosphate (Pi). Which of the following processes would be most severely limited?

A.Carbon fixation by RuBisCOB.ATP synthesis and regeneration of RuBP in the Calvin cycleC.Absorption of photons by chlorophyllD.Splitting of water molecules in Photosystem II

Question 8

A researcher adds an uncoupler to mitochondria. The uncoupler makes the inner mitochondrial membrane freely permeable to protons (H⁺). Which of the following would be the immediate result?

A.ATP synthesis increases because more protons flow through ATP synthaseB.The electron transport chain stops because it has no electron acceptorsC.The proton gradient collapses and ATP synthesis via oxidative phosphorylation haltsD.NADH accumulates because the Krebs cycle accelerates

Question 9

An athlete sprinting at maximum effort for 8 seconds relies primarily on which metabolic process to generate ATP?

A.Aerobic cellular respiration (oxidative phosphorylation)B.Fermentation producing ethanolC.Phosphocreatine hydrolysis and glycolysis (anaerobic)D.Beta-oxidation of fatty acids

Question 10

During the Krebs cycle, one turn (per acetyl-CoA) produces which of the following sets of energy carriers?

A.2 NADH, 1 FADH₂, 1 ATP (or GTP)B.3 NADH, 1 FADH₂, 1 ATP (or GTP)C.3 NADH, 2 FADH₂, 2 ATPD.2 NADH, 2 FADH₂, 1 ATP (or GTP)

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Question 11

During the light-dependent reactions of photosynthesis, which molecule directly receives the electrons energized by absorbed photons?

A.NADPHB.The primary electron acceptor within the photosystemC.ATP synthaseD.Carbon dioxide

Question 12

In the light reactions, the electron transport chain between Photosystem II and Photosystem I pumps protons into the thylakoid lumen. What is the primary function of this proton gradient?

A.To reduce NADP⁺ to NADPH directlyB.To drive ATP synthesis through ATP synthase (chemiosmosis)C.To split water molecules and release oxygenD.To absorb additional photons for Photosystem I

AP Biology Unit 3: Cellular Energetics — Free with Answer Explanations | Test Practice Hub