After an intense sprint, a runner experiences painful cramps in the leg muscles. Explain the biochemical reason for this, tracing the exact pathway that leads to cramp formation.
Generated by claude-sonnet-4-6 · 2026-06-26 01:00 · grounding rag
Model Answer
During an intense sprint, muscles require more energy than oxygen can supply. When oxygen is insufficient, muscles switch from aerobic respiration to anaerobic respiration.
In anaerobic respiration, glucose is incompletely broken down:
Glucose → Lactic acid + Energy
Lactic acid accumulates in the muscle tissue. This build-up of lactic acid causes a drop in muscle pH and interferes with muscle contraction, leading to painful cramps. The cramps persist until the lactic acid is removed through the bloodstream and broken down once oxygen supply is restored.
Source: Life Processes, Chapter 1 (Respiration)
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Explanation
- The question tests anaerobic respiration in muscles — a key concept from Chapter 1 (Life Processes), not Chapter 6. The source passages provided do not cover this, but a CBSE student must answer from the prescribed textbook content.
- Key terms examiners look for: anaerobic respiration, lactic acid accumulation, lack of oxygen/insufficient oxygen supply.
- The pathway must be clearly stated: oxygen deficit → anaerobic pathway → lactic acid build-up → cramps.
- Do NOT write aerobic respiration here; the whole point is the switch to anaerobic.
- Three marks = three distinct points: (1) oxygen deficit, (2) anaerobic respiration/lactic acid formed, (3) lactic acid causes cramps.