Q1. [3] medium thorough-understanding
Both aerobic and anaerobic respiration begin with the same glucose molecule, yet aerobic respiration releases far more ATP. Explain why, referring to what happens to the pyruvate produced in glycolysis under each condition.
Generated by claude-sonnet-4-6 · 2026-06-26 01:00 · grounding rag
Model Answer
Both aerobic and anaerobic respiration begin with glycolysis in the cytoplasm, where glucose is broken down into pyruvate, producing a small amount of ATP.
- Aerobic respiration: Pyruvate is taken into the mitochondria and completely broken down into carbon dioxide and water. This releases a large amount of energy as ATP.
- Anaerobic respiration: Pyruvate is not fully broken down. It is converted into ethanol and CO₂ (in yeast) or lactic acid (in muscles) in the cytoplasm itself, releasing only a small amount of ATP.
Since aerobic respiration completely oxidises pyruvate, it extracts far more energy from each glucose molecule than anaerobic respiration.
Source: Life Processes, Chapter 5 (Respiration section)
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Explanation
- The examiner wants you to mention glycolysis as the common first step, then contrast what happens to pyruvate under each condition.
- Key fact from the textbook: "breakdown of pyruvate to give CO₂, water and energy takes place in the mitochondria" (Exercise Q4) — always mention mitochondria for aerobic.
- The textbook states "aerobic respiration makes more energy available" — use this exact idea.
- Avoid over-explaining; three crisp points (common step → aerobic fate → anaerobic fate) are enough for 3 marks.