What an AP Bio Cellular Respiration Quiz Covers
An AP Biology cellular respiration quiz tests your grasp of how cells extract energy from glucose. Expect questions on glycolysis, the Krebs cycle, oxidative phosphorylation, and the total ATP yield. The quiz format often mixes multiple-choice items with free-response prompts that ask you to trace carbon flow, predict the effect of inhibitors, or compare aerobic and anaerobic pathways. Mastering the location of each stage, the inputs and outputs, and the role of NADH and FADH2 is essential for a strong score.
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Key Stages and What Gets Asked
Most quizzes break cellular respiration into its major phases. Glycolysis occurs in the cytoplasm and converts one glucose into two pyruvate molecules, yielding a net of 2 ATP and 2 NADH. The link reaction then moves pyruvate into the mitochondrial matrix, where it becomes acetyl-CoA and releases CO2. The Krebs cycle per turn generates 3 NADH, 1 FADH2, 1 GTP, and 2 CO2; because two turns occur per glucose, the totals double. The electron transport chain and chemiosmosis, located in the inner mitochondrial membrane, use electrons from NADH and FADH2 to pump protons and drive ATP synthase, producing roughly 32 to 34 ATP.
Common Question Types
- Identifying the stage and location of a given reaction
- Calculating net ATP yield from glucose under aerobic conditions
- Predicting the effect of cyanide or oligomycin on the ETC
- Comparing the output of aerobic respiration to fermentation
ATP Yield and Common Traps
Students frequently mix up the gross and net ATP counts. Glycolysis produces 4 ATP but consumes 2, so the net is 2. The Krebs cycle itself yields only 2 GTP (equivalent to ATP) per glucose; the bulk of ATP comes from oxidative phosphorylation. Many quizzes also test whether you can account for the ATP cost of transporting NADH from the cytoplasm into the mitochondria via shuttle systems, which reduces the total yield depending on whether the malate-aspartate or glycerol-3-phosphate shuttle is used.
| Stage | Location | ATP (net per glucose) | NADH | FADH2 |
|---|---|---|---|---|
| Glycolysis | Cytoplasm | 2 | 2 | 0 |
| Pyruvate oxidation | Mitochondrial matrix | 0 | 2 | 0 |
| Krebs cycle | Mitochondrial matrix | 2 GTP | 6 | 2 |
| Oxidative phosphorylation | Inner membrane | ~32–34 | — | — |
Anaerobic Pathways and Fermentation
Quizzes often contrast aerobic respiration with fermentation. Under anaerobic conditions, cells regenerate NAD+ through lactate fermentation in animals or ethanol fermentation in yeast, allowing glycolysis to continue but yielding only 2 ATP per glucose. Questions may ask you to explain why fermentation is far less efficient, or to describe the ecological contexts in which organisms rely on these pathways.
Study Strategies for the Quiz
Effective preparation starts with drawing the entire pathway from memory, labeling every enzyme, carrier, and location. Then, practice tracing a single carbon atom from glucose to CO2 and following the electrons from glucose to final electron acceptor oxygen. Work through past AP free-response questions that ask you to predict changes in ATP or NADH levels when a specific inhibitor is added, and always check your reasoning against the stoichiometry of each stage.