AP Biology: Cellular Energetics Practice Questions
Test yourself on Cellular Energetics with 12 original AP Exams practice questions. Pick an answer to see instant feedback and a full explanation.
Free original practice questions for study purposes. Open Exam Prep is an independent study resource and is not affiliated with, endorsed by, or sponsored by the makers of AP Exams.
advertisement
Answer the questions below — you get instant feedback and a full explanation for each.
1. A student compares two reactions. Reaction 1 releases free energy, while Reaction 2 requires a net input of free energy. Which statement best describes the reactions?
Explanation. An exergonic reaction has a negative change in free energy and releases energy. An endergonic reaction has a positive change in free energy and requires energy input, often coupled to ATP hydrolysis in cells.
2. Which role of an enzyme most directly explains why reactions can occur faster at normal cellular temperatures?
Explanation. Enzymes speed reactions by lowering activation energy, the energy barrier needed to reach the transition state. They do not change the overall free-energy difference between reactants and products and are not consumed.
3. During cellular respiration, most ATP is produced by oxidative phosphorylation. What directly drives ATP synthase in this process?
Explanation. The electron transport chain pumps protons across the inner mitochondrial membrane. As protons flow back through ATP synthase, the enzyme uses that electrochemical gradient to phosphorylate ADP to ATP.
4. A poison makes the inner mitochondrial membrane freely permeable to protons. Which outcome is most likely?
Explanation. If protons can leak across the inner membrane, the proton gradient collapses. ATP synthase then has less stored electrochemical energy to use, so oxidative phosphorylation produces much less ATP.
5. In glycolysis, one glucose molecule is converted into two molecules of pyruvate. What is the net ATP gain from glycolysis per glucose?
Explanation. Glycolysis uses 2 ATP in its investment phase and produces 4 ATP in its payoff phase, for a net gain of 2 ATP per glucose. It also produces NADH and pyruvate.
6. Which statement correctly compares fermentation with aerobic respiration?
Explanation. When oxygen is unavailable, fermentation transfers electrons from NADH to organic molecules, regenerating NAD+. This allows glycolysis to continue making a small amount of ATP without the electron transport chain.
7. In photosynthesis, what is the main function of the light reactions?
Explanation. The light reactions capture light energy and produce ATP and NADPH. Those molecules then provide energy and reducing power for the Calvin cycle, where carbon dioxide is fixed into carbohydrate.
8. A plant cell is exposed to a herbicide that blocks electron flow through photosystem II. Which direct effect would be expected first?
Explanation. Photosystem II begins the photosynthetic electron transport chain and helps create the proton gradient used to make ATP. Blocking it reduces electron flow, lowering ATP and NADPH production and eventually slowing the Calvin cycle.
9. The Calvin cycle is sometimes called the light-independent reactions. Which input is directly required for carbon fixation in the Calvin cycle?
Explanation. Carbon fixation in the Calvin cycle begins when carbon dioxide is attached to RuBP by the enzyme rubisco. ATP and NADPH from the light reactions power later steps, but carbon dioxide is the carbon source.
10. A graph shows that an enzyme works best at pH 7, but its activity is very low at pH 3. Which explanation is most likely?
Explanation. Extreme pH can disrupt ionic and hydrogen bonds that help maintain protein shape. If the active site changes shape, substrate binding and catalysis decrease. Enzymes have optimal ranges rather than working equally in all conditions.
11. Which observation best supports the claim that ATP hydrolysis can be coupled to endergonic cellular work?
Explanation. ATP hydrolysis can transfer a phosphate group to a protein, changing the protein's shape and making cellular work possible. Active transport pumps, for example, often use phosphorylation to move substances against gradients.
12. A muscle cell suddenly has a high demand for ATP. Which change would most directly increase ATP production through aerobic respiration if oxygen is available?
Explanation. With oxygen available, faster electron transport can pump more protons across the inner mitochondrial membrane, strengthening the gradient that drives ATP synthase. Blocking ADP use or pyruvate entry would reduce ATP output.
📘 Want a full structured course and official-style practice tests? Browse top-rated AP Exams prep books and courses. Some links are affiliate links; we may earn a commission at no cost to you.
advertisement
FAQ
What is the fastest way to review cellular energetics for AP Biology?
Focus on cause-and-effect links: enzyme structure affects reaction rate, proton gradients drive ATP synthase, oxygen accepts electrons in respiration, and ATP/NADPH from the light reactions power the Calvin cycle.
Do I need to memorize every step of glycolysis and the Krebs cycle?
You should know the major inputs, outputs, locations, and purpose of each stage. AP Biology questions usually emphasize energy transfer, redox carriers, gradients, and experimental reasoning more than memorizing every intermediate.
What mistakes are common on cellular energetics questions?
Common mistakes include thinking enzymes change the final free energy of a reaction, forgetting that fermentation mainly regenerates NAD+, and mixing up the light reactions with the Calvin cycle.