Rucete ✏ AP Biology In a Nutshell
7. Cellular Respiration — Practice Questions 2
This chapter explains how cells extract energy from glucose through glycolysis, pyruvate oxidation, the Krebs cycle, oxidative phosphorylation, and fermentation.
Need a quick review?
📘 Go to the Concept Summary
(Multiple Choice — Click to Reveal Answer)
1. What is the first molecule that enters glycolysis?
(A) Pyruvate
(B) Glucose
(C) Acetyl-CoA
(D) NAD+
Answer
(B) — Glycolysis begins with the six-carbon molecule glucose.
2. In which part of the cell does oxidative phosphorylation occur?
(A) Cytosol
(B) Inner mitochondrial membrane
(C) Mitochondrial matrix
(D) Outer mitochondrial membrane
Answer
(B) — Oxidative phosphorylation occurs along the inner membrane of mitochondria.
3. Which molecule directly powers ATP synthase to produce ATP?
(A) Oxygen
(B) NADH
(C) Proton (H⁺) flow
(D) Carbon dioxide
Answer
(C) — The flow of protons through ATP synthase provides the energy for ATP production.
4. What happens to pyruvate in the absence of oxygen in human muscle cells?
(A) It enters the Krebs cycle.
(B) It is converted to lactic acid.
(C) It forms ethanol.
(D) It breaks down into carbon dioxide.
Answer
(B) — In anaerobic conditions, pyruvate is converted into lactic acid through fermentation.
5. Which carrier molecule transports high-energy electrons from the Krebs cycle to the electron transport chain?
(A) ATP
(B) Oxygen
(C) NADH
(D) Pyruvate
Answer
(C) — NADH carries high-energy electrons to the electron transport chain.
6. What is produced as a waste product at the end of the electron transport chain?
(A) Carbon dioxide
(B) Water
(C) Glucose
(D) ATP
Answer
(B) — Water is formed when oxygen accepts electrons and combines with protons.
7. What is the primary role of NADH and FADH₂ in cellular respiration?
(A) To split glucose
(B) To carry high-energy electrons to the electron transport chain
(C) To produce oxygen
(D) To store carbon dioxide
Answer
(B) — NADH and FADH₂ deliver high-energy electrons to the electron transport chain.
8. How many carbon atoms are in a molecule of pyruvate?
(A) 6
(B) 5
(C) 3
(D) 2
Answer
(C) — Pyruvate is a three-carbon molecule formed during glycolysis.
9. Which process does not require oxygen to produce ATP?
(A) Electron transport chain
(B) Krebs cycle
(C) Glycolysis
(D) Oxidative phosphorylation
Answer
(C) — Glycolysis occurs in the cytosol and does not require oxygen.
10. During glycolysis, glucose is ultimately split into two molecules of:
(A) Acetyl-CoA
(B) NADH
(C) Pyruvate
(D) FADH₂
Answer
(C) — Glycolysis breaks glucose into two molecules of pyruvate.
11. What is the main energy currency produced by cellular respiration?
(A) NADPH
(B) ATP
(C) FADH₂
(D) Glucose
Answer
(B) — ATP is the primary energy currency generated through cellular respiration.
12. Which stage of cellular respiration releases the most carbon dioxide?
(A) Glycolysis
(B) Krebs cycle
(C) Electron transport chain
(D) Chemiosmosis
Answer
(B) — The Krebs cycle produces most of the CO₂ released during cellular respiration.
13. In which cellular compartment does glycolysis occur?
(A) Mitochondrial matrix
(B) Cytoplasm
(C) Nucleus
(D) Inner mitochondrial membrane
Answer
(B) — Glycolysis occurs in the cytoplasm (cytosol) of the cell.
14. Which molecule is regenerated at the end of the Krebs cycle to allow the cycle to continue?
(A) Acetyl-CoA
(B) Citrate
(C) Oxaloacetate
(D) Pyruvate
Answer
(C) — Oxaloacetate is regenerated to combine with Acetyl-CoA and restart the Krebs cycle.
15. How many ATP molecules (net) are produced during glycolysis from one glucose molecule?
(A) 2
(B) 4
(C) 6
(D) 8
Answer
(A) — Glycolysis has a net production of 2 ATP per glucose molecule.
16. What gas is required as the final electron acceptor in aerobic cellular respiration?
(A) Nitrogen
(B) Carbon dioxide
(C) Oxygen
(D) Hydrogen
Answer
(C) — Oxygen accepts electrons at the end of the electron transport chain, forming water.
17. Which of the following produces ATP without directly involving an electron transport chain?
(A) Oxidative phosphorylation
(B) Glycolysis
(C) Chemiosmosis
(D) Electron transport
Answer
(B) — Glycolysis produces ATP through substrate-level phosphorylation, without an electron transport chain.
18. What is the fate of the oxygen consumed during cellular respiration?
(A) It becomes part of glucose.
(B) It accepts electrons and protons to form water.
(C) It is released as carbon dioxide.
(D) It powers ATP synthase directly.
Answer
(B) — Oxygen combines with electrons and protons at the end of the electron transport chain to form water.
19. What two products are generated when pyruvate is converted into acetyl-CoA?
(A) NADH and carbon dioxide
(B) FADH₂ and glucose
(C) Oxygen and ATP
(D) Water and NAD+
Answer
(A) — Pyruvate oxidation produces NADH and releases carbon dioxide.
20. What happens to most of the energy extracted from glucose during glycolysis and the Krebs cycle?
(A) It is used immediately to make ATP.
(B) It is stored in NADH and FADH₂.
(C) It is released as heat.
(D) It forms glucose polymers.
Answer
(B) — Most of the energy is captured in the form of NADH and FADH₂.
21. During oxidative phosphorylation, where do protons accumulate before flowing through ATP synthase?
(A) Cytoplasm
(B) Mitochondrial matrix
(C) Intermembrane space
(D) Outer mitochondrial membrane
Answer
(C) — Protons are pumped into the intermembrane space, creating the proton gradient.
22. Which process generates carbon dioxide as a waste product?
(A) Glycolysis
(B) Fermentation
(C) Krebs cycle
(D) Chemiosmosis
Answer
(C) — The Krebs cycle releases CO₂ during the oxidation of carbon compounds.
23. Which of the following is true about fermentation?
(A) It requires oxygen.
(B) It produces much more ATP than oxidative phosphorylation.
(C) It regenerates NAD+ for glycolysis.
(D) It occurs only in the mitochondria.
Answer
(C) — Fermentation regenerates NAD+ to allow glycolysis to continue under anaerobic conditions.
24. In alcohol fermentation, what is the final electron acceptor?
(A) Oxygen
(B) Acetaldehyde
(C) NAD+
(D) Carbon dioxide
Answer
(B) — In alcohol fermentation, acetaldehyde accepts electrons from NADH to form ethanol.
25. What enzyme complex links glycolysis to the Krebs cycle by processing pyruvate?
(A) ATP synthase
(B) Rubisco
(C) Pyruvate dehydrogenase
(D) Cytochrome oxidase
Answer
(C) — Pyruvate dehydrogenase converts pyruvate into acetyl-CoA for entry into the Krebs cycle.
26. What would occur if the mitochondrial inner membrane became permeable to protons?
(A) Increased ATP production
(B) Disruption of the proton gradient, reducing ATP synthesis
(C) Enhanced NADH oxidation
(D) Faster electron transport
Answer
(B) — A leaky membrane would dissipate the proton gradient, reducing ATP production.
27. Which step produces the greatest number of reduced electron carriers during cellular respiration?
(A) Glycolysis
(B) Pyruvate oxidation
(C) Krebs cycle
(D) Electron transport chain
Answer
(C) — The Krebs cycle generates the most NADH and FADH₂ molecules.
28. If a toxin blocks ATP synthase, what will happen to the proton gradient across the inner mitochondrial membrane?
(A) It will dissipate rapidly.
(B) It will continue to build up.
(C) It will reverse direction.
(D) It will enhance ATP production.
Answer
(B) — Without ATP synthase using the protons, the proton gradient will continue accumulating.
29. In the absence of oxygen, which step of cellular respiration is directly impacted first?
(A) Glycolysis
(B) Krebs cycle
(C) Electron transport chain
(D) Chemiosmosis
Answer
(C) — Without oxygen as the final electron acceptor, the electron transport chain halts first.
30. Why does fermentation allow glycolysis to continue under anaerobic conditions?
(A) It produces ATP by oxidative phosphorylation.
(B) It regenerates NAD+ needed for glycolysis.
(C) It synthesizes glucose.
(D) It breaks down oxygen molecules.
Answer
(B) — Fermentation regenerates NAD+ by oxidizing NADH, keeping glycolysis running.
31. Which of the following best describes chemiosmosis in mitochondria?
(A) Movement of water across the mitochondrial membrane
(B) Movement of protons through ATP synthase to generate ATP
(C) Transfer of electrons directly to ATP
(D) Synthesis of glucose from carbon dioxide
Answer
(B) — Chemiosmosis refers to the flow of protons through ATP synthase to drive ATP synthesis.
32. Which stage of cellular respiration releases water as a byproduct?
(A) Glycolysis
(B) Krebs cycle
(C) Electron transport chain
(D) Pyruvate oxidation
Answer
(C) — Water is formed at the end of the electron transport chain when oxygen accepts electrons and protons.
33. How does cyanide poisoning disrupt cellular respiration?
(A) It blocks glycolysis.
(B) It prevents the regeneration of NAD+.
(C) It inhibits electron transfer to oxygen.
(D) It destroys glucose molecules directly.
Answer
(C) — Cyanide blocks the final step of electron transfer to oxygen, stopping ATP production.
34. If NAD+ is unavailable, what immediate effect would occur in glycolysis?
(A) Glycolysis would speed up.
(B) Pyruvate would be converted to acetyl-CoA faster.
(C) Glycolysis would stop.
(D) Oxygen would be rapidly consumed.
Answer
(C) — Without NAD+, glycolysis cannot proceed because no carrier would accept electrons.
35. Which statement best explains why fats produce more ATP than carbohydrates when oxidized?
(A) Fats contain fewer hydrogen atoms.
(B) Fats release carbon dioxide more easily.
(C) Fats have more hydrogen atoms to donate electrons.
(D) Fats directly enter the electron transport chain.
Answer
(C) — Fats have many hydrogen atoms, providing abundant high-energy electrons for ATP production.
36. Explain why the electron transport chain requires oxygen to function properly.
Answer
Oxygen acts as the final electron acceptor, allowing the flow of electrons through the chain; without oxygen, electron flow halts and ATP synthesis stops.
37. How does the structure of the inner mitochondrial membrane enhance its function in cellular respiration?
Answer
The inner membrane's folds (cristae) increase surface area, providing more space for electron transport chains and ATP synthase, boosting ATP production.
38. Describe the role of ATP synthase in oxidative phosphorylation.
Answer
ATP synthase uses the energy of protons moving down their concentration gradient to catalyze the conversion of ADP and inorganic phosphate into ATP.
39. Predict the immediate effect if a cell's mitochondria lost their proton gradient.
Answer
Without a proton gradient, ATP synthase would be unable to function, leading to a rapid decrease in ATP production.
40. Explain the main advantage of aerobic respiration compared to fermentation.
Answer
Aerobic respiration produces significantly more ATP per glucose molecule (~32 ATP) compared to fermentation (only 2 ATP), providing more energy efficiency.
41. Why is glycolysis considered an ancient metabolic pathway?
Answer
Glycolysis occurs in the cytoplasm and does not require oxygen, suggesting it evolved early before oxygen was abundant in Earth's atmosphere.
42. How does the absence of oxygen affect the function of the Krebs cycle?
Answer
Without oxygen to accept electrons at the end of the electron transport chain, NADH and FADH₂ cannot unload electrons, causing the Krebs cycle to stop.
43. Compare the efficiency of ATP production between oxidative phosphorylation and substrate-level phosphorylation.
Answer
Oxidative phosphorylation produces the majority of ATP via chemiosmosis, while substrate-level phosphorylation generates much less ATP during glycolysis and the Krebs cycle.
44. Describe the energy transformations that occur during glycolysis.
Answer
Chemical energy stored in glucose bonds is partially transferred to ATP and NADH during glycolysis.
45. What would happen to ATP production if NADH levels were severely depleted?
Answer
Electron flow through the electron transport chain would decrease, reducing proton pumping and ATP synthesis.
46. Explain the role of acetyl-CoA in cellular respiration.
Answer
Acetyl-CoA delivers two-carbon units to the Krebs cycle, where they are oxidized for energy extraction through the production of NADH, FADH₂, and ATP.
47. Why does lactic acid fermentation occur in muscle cells under anaerobic conditions?
Answer
When oxygen is scarce, lactic acid fermentation regenerates NAD+ needed for glycolysis to continue producing small amounts of ATP.
48. How does cyanide cause rapid death at the cellular level?
Answer
Cyanide inhibits the transfer of electrons to oxygen, halting the electron transport chain and stopping ATP production, leading to cell death.
49. In what way is chemiosmosis similar in mitochondria and chloroplasts?
Answer
In both organelles, a proton gradient across a membrane drives ATP synthesis through ATP synthase.
50. Summarize the overall chemical equation for cellular respiration.
Answer
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP (energy).