Q1. [3]
Complete the pathways given below, showing the breakdown of glucose. Identify 'A', 'B', 'C', 'D', 'E' and 'F'.
Previously asked in CBSE board exam
2026 31/2/1 Q13
Generated by claude-sonnet-4-6 · 2026-06-11 09:52 · grounding rag
Model Answer
A = Glucose (6-carbon molecule) breaks down in the cytoplasm into B = Pyruvate (3-carbon molecule).
Pyruvate then follows two pathways:
Anaerobic pathway:
- In yeast: Pyruvate → C = Ethanol + D = Carbon dioxide (fermentation)
- In muscles (lack of O₂): Pyruvate → E = Lactic acid
Aerobic pathway:
- In mitochondria (presence of O₂): Pyruvate → F = Carbon dioxide + Water + Energy (ATP)
Source: Chapter 5, Section 5.3 — Respiration
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Explanation
The examiner expects students to recall Figure 5.8 (Break-down of glucose by various pathways) from the textbook. Key points to remember:
- A and B are always the same regardless of pathway — glucose → pyruvate in cytoplasm.
- C & D are the anaerobic products in yeast (ethanol + CO₂).
- E is the anaerobic product in muscle cells (lactic acid — causes cramps).
- F represents aerobic end-products in mitochondria (CO₂ + H₂O + energy).
- Mention location (cytoplasm/mitochondria/yeast) for full marks.
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