Explain how and why ventilation rate varies with exercise.

during exercise the rate of tissue respiration increases/more carbon dioxide produced;

carbon dioxide production in the tissues exceeds the rate of breathing it out;

increase in carbonic acid / increase in H\(^ + \) ions / pH drops in the blood plasma;

lactic acid (in strenuous exercise) reduces pH;

chemoreceptors/chemosensors detect change in pH/increase in carbon dioxide/ decrease in oxygen;

receptors in the carotid/aortic bodies;

nerve impulses sent to the breathing centres of the brain;

nerve impulses then sent to diaphragm/intercostal muscles;

negative feedback control;

Many candidates, that had studied this in detail, could explain how and why ventilation rate varies with exercise in detail, with many candidates gaining four or five marks here.