Which stage of cellular respiration produces the largest amount of ATP?

Answer: Oxidative phosphorylation in the electron transport chain Glycolysis and Krebs each produce a small ATP yield (substrate-level), but most ATP comes from oxidative phosphorylation, where ETC-driven proton gradients power ATP synthase.

The overall equation for aerobic cellular respiration is

Answer: C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + ATP Glucose is oxidized to CO₂; O₂ is the terminal electron acceptor reduced to water; energy captured as ATP.

Which biological reasoning best explains the trend?

Answer: Higher temperature increases molecular kinetic energy and enzyme-substrate collisions, raising respiration rate. Within tolerance limits, raising temperature accelerates enzyme-catalyzed reactions because molecules collide more frequently and forcefully.

AP Biology · Topic 3.6

Cellular Respiration Practice

Part of Cellular Energetics.(ENE-1.Q)

Practice questions

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Sample questions

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Sample 1difficulty 1/5
$The flowchart summarizes the four stages of aerobic cellular respiration.$
$Which stage of cellular respiration produces the largest amount of ATP?$
- A
  $Glycolysis in the cytoplasm$
- B
  $Pyruvate oxidation$
- C
  $Oxidative phosphorylation in the electron transport chain$
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- D
  $Krebs cycle by substrate-level phosphorylation$
Why
$Glycolysis and Krebs each produce a small ATP yield (substrate-level), but most ATP comes from oxidative phosphorylation, where ETC-driven proton gradients power ATP synthase.$
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Sample 2difficulty 1/5
$The overall equation for aerobic cellular respiration is$
- A
  $6 CO₂ + 6 H₂O + light \to C₆H₁₂O₆ + 6 O₂$
- B
  $2 ATP + 2 ATP \to glucose + 4 ADP + Pi$
- C
  $Glucose + ADP + Pi \to 2 lactate + heat$
- D
  $C₆H₁₂O₆ + 6 O₂ \to 6 CO₂ + 6 H₂O + ATP$
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Why
$Glucose is oxidized to CO₂; O₂ is the terminal electron acceptor reduced to water; energy captured as ATP.$
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Sample 3difficulty 2/5
$Germinating pea seeds were placed in respirometers held in water baths at 5, 15, 25, and 35 degrees C. Volume of O2 consumed per gram of seed per minute was recorded after a 5-minute equilibration.$
$Which biological reasoning best explains the trend?$
- A
  $Seeds at higher temperature reproduce faster, increasing biomass.$
- B
  $Higher temperature increases molecular kinetic energy and enzyme-substrate collisions, raising respiration rate.$
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- C
  $Oxygen solubility increases at higher temperature.$
- D
  $Cold temperatures denature respiration enzymes.$
Why
$Within tolerance limits, raising temperature accelerates enzyme-catalyzed reactions because molecules collide more frequently and forcefully.$
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Sample 4difficulty 2/5
$Glycolysis occurs in the$
- A
  $Cytoplasm (cytosol)$
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- B
  $Inner mitochondrial membrane$
- C
  $Nucleus$
- D
  $Mitochondrial matrix$
Why
$Glycolysis is anaerobic and predates the eukaryote-mitochondrion relationship; it happens in cytosol.$
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Sample 5difficulty 2/5
$The pathway compares two fermentation routes used when oxygen is unavailable.$
$What is the primary purpose of the reactions that convert pyruvate to lactic acid or ethanol?$
- A
  $Reducing oxygen to water$
- B
  $Producing CO2 for the Calvin cycle$
- C
  $Regenerating NAD+ so glycolysis can continue producing ATP$
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- D
  $Generating an additional 30 ATP per glucose$
Why
$Without O2, the ETC cannot reoxidize NADH. Fermentation oxidizes NADH back to NAD+, allowing glycolysis to keep generating ATP.$
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