Cellular Respiration

Cellular Respiration is topic 3.6 of AP Biology, inside Cellular Energetics. This page works through three real practice questions on it, with the full reasoning behind each credited answer.

Practise this topic freeThe whole unit
79 questionsConcept Explanation51% with a figure
Worked examples

Three real cellular respiration questions

From the practice pool, not the mock papers — each with the reasoning that produces the answer.

79 practice questions sit on this single topic — enough that it is worth working through by topic rather than meeting it scattered through a unit review.

51% of them come with a figure. Reading the graph or diagram correctly is most of the work here before any content knowledge applies.

Concept Explanation

During oxidative phosphorylation, what directly drives ATP synthase to produce ATP?

  1. AFlow of protons down their electrochemical gradientcorrect
  2. BHydrolysis of DNA in the mitochondrial matrix
  3. CDirect attachment of oxygen to glucose in the cytosol
  4. DMovement of electrons through the plasma membrane of the cell
Why A is correct

ATP synthase uses the energy of protons flowing down their electrochemical gradient across the inner mitochondrial membrane to synthesize ATP.

The stem asks students to explain a specific mechanism, not just recall a unit term: "During oxidative phosphorylation, what directly drives ATP synthase to produce ATP". The correct choice is supported by ATP synthase uses the energy of protons flowing down their electrochemical gradient across the inner mitochondrial membrane to synthesize ATP. The tempting alternatives such as Hydrolysis of DNA in the mitochondrial matrix or Direct attachment of oxygen to glucose in the cytosol fail because they do not produce the same outcome described in the stem.

Questions and Methods · with figure

A student wants to test whether yeast cells produce carbon dioxide faster when glucose concentration is increased. Which design is most appropriate?

  1. AUse only water and yeast because glucose is not relevant to fermentation.
  2. BUse equal yeast amounts with several glucose concentrations and repeat each treatment.correct
  3. CUse one tube with glucose and record the final gas height only once.
  4. DUse different yeast masses in each tube and keep glucose concentration constant.
Why B is correct

A valid design varies the independent variable, glucose concentration, while controlling yeast amount and measuring the dependent variable with replication.

This prompt is testing design logic in the scenario "A student wants to test whether yeast cells produce carbon dioxide faster when glucose concentration is increased....". A complete explanation should identify the changed factor, the measured response, and Which design is most appropriate? A valid design varies the independent variable,... before interpreting the outcome. The item-specific reasoning is A valid design varies the independent variable, glucose concentration, while controlling yeast amount and measuring the dependent variable with replication.

Questions and Methods · with figure

A student wants to test whether germinating seeds consume more oxygen than dormant seeds. Which design best addresses the question?

  1. AUse no seeds because oxygen consumption cannot be measured indirectly.
  2. BUse different temperatures for each seed group and measure only the final seed mass.
  3. CUse equal masses of germinating and dormant seeds with replicated respirometers at the same temperature.correct
  4. DUse only dormant seeds and compare two unrelated plant species.
Why C is correct

A valid comparison controls seed mass and temperature, varies seed state, measures oxygen consumption, and includes replication. The independent variable is seed state, germinating versus dormant, and the dependent variable is oxygen consumption.

This prompt is testing design logic in the scenario "A student wants to test whether germinating seeds consume more oxygen than dormant seeds. Which design best...". A complete explanation should change or compare seed state, germinating versus dormant, then measure oxygen consumption before interpreting the outcome. The item-specific reasoning is A valid comparison controls seed mass and temperature, varies seed state, measures oxygen consumption, and includes replication. The independent variable is seed state, germinating versus dormant, and the dependent variable is oxygen consumption

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Last reviewed 2026-08-28. Topic and unit names follow the College Board course framework. Question counts describe the PrepScore practice bank, not the exam.
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Work cellular respiration until the reasoning is automatic.

Real AP questions with a full explanation on every answer, and a mistake bank that only clears when you get it right.

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