The graph shows how a student’s breathing rate changed during and after exercise. Calculate how long it took after he finished his exercise for his breathing to return to normal.

We know that the respiratory rate increases during exercise. According to the graph, The breathing rate of the student started to increase after he did exercise, from 12 breaths per minute to 25 breaths per min. He stopped doing exercise on the eleventh minute and the breathing rate became normal on 16th minute. Thus, we can say that the breathing rate became normal after five minutes.

The graph shows how a student’s breathing rate changed during and after exercise. Explain why his breathing rate does not return to normal immediately after he stopped exercise.

Since the demand of the body for oxygen is increased and the muscles need more amount of energy to do exercise. The glucose (C 6 H 12 O 6 ) in the muscles is oxidised as fast as possible by the cells. Thus, they need more oxygen. So during exercise, to cope up with the need of the body, the muscles start oxidising glucose by anaerobic respiration. It results in the accumulation of lactic acid. At this stage, the body is under oxygen debt. It requires oxygen to return the body to normal. So as the boy stops doing exercise, the amount of oxygen required to remove the lactic acid is utilised. Thus, the respiratory rate and heart rate does not come to normal straight away.

The graph shows how a student’s breathing rate changed during and after exercise. Describe and explain how would you expect the student's heart rate to change during the 16-minute period shown on the graph.

The demand of the body for oxygen is increased during exercise because the metabolism is increased. Since the muscles need more amount of energy to do exercise. The glucose (C 6 H 12 O 6 ) in the muscles is oxidised as fast as possible by the cells to release energy. Thus, they need more oxygen. During exercise, to cope up with the need of a body, the blood circulation also increases so that supply of oxygen is not hampered. From the given graph we can see that the respiratory rate of the student is increasing from 12 breaths per minute to a maximum of 25 breaths per minute. As he breathes fast and deeply, we can say that the heart rate will also increase as he continues doing exercise. Initially, the heart rate is low which will become maximum at the 5th minute and starts decreasing after the 14th minute.