After a period of intense exercise, a person continues to breathe deeply and rapidly for several minutes even though the exercise has stopped. Explain why this happens in terms of anaerobic respiration and its products.

During intense exercise the oxygen supply to the working muscles is insufficient, so the cells respire anaerobically. The anaerobic pathway produces lactic acid, which accumulates in the muscle tissue. The build‑up of lactic acid creates an oxygen debt – the amount of oxygen that would have been required to fully oxidise the glucose used. After the exercise stops, the person continues to breathe deeply and rapidly to increase the oxygen supply. The extra oxygen is used to convert the lactic acid back to pyruvate and then to CO₂ and H₂O, thereby repaying the oxygen debt.