In the last minutes of a football match, Imran sprints again and again.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
In the last minutes of a football match, Imran sprints again and again. His thigh muscles start to ache and cramp. Explain what has happened in his muscle cells. Why does the ache fade after he rests and breathes deeply for a while?
Need a reminder? The key ideaShow
Respiration releases the energy of glucose. Glucose is split into pyruvate in the cytoplasm. Without oxygen, yeast makes ethanol and carbon dioxide, and muscles make lactic acid: about 2 ATP for each glucose. With oxygen, in the mitochondria, pyruvate becomes carbon dioxide and water: about 38 ATP for each glucose.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Too little oxygen. While he sprints, his muscles use oxygen faster than the blood can bring it.
Step 2. Anaerobic respiration. Without enough oxygen, pyruvate in the muscle cells changes into lactic acid. Little energy is released.
Step 3. The cramp. Lactic acid builds up in the muscles and causes the ache and the cramp.
Step 4. Rest. Resting and deep breathing bring plenty of oxygen back to the muscles. The lactic acid is then broken down and removed.
Answer: his muscles respired without enough oxygen and made lactic acid, which caused the cramp; extra oxygen after the match lets the body clear the lactic acid.
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