Horses are mammals that have similar breathing and circulatory systems to humans. The heart rate of a horse was monitored before, during and after a race. Figure 4.1 shows the results.

Figure 4.1, a plotted graph of heart rate / beats per minute (0 to 200) against time / minutes (0 to 8), with arrows marking race starts at 1 minute and race ends at 4 minutes: 40 at 0 and 1 minute, 180 at 2, 3 and 4 minutes, then 120 at 5, 80 at 6, and 40 at 7 and 8 minutes

4(a)Interpreting Data Drawing ConclusionsMedium3 marks

Describe the results shown in Figure 4.1.

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4(b)(i)Aerobic Anaerobic RespirationEasy2 marks

During the race the rate of respiration changes. State the balanced equation for aerobic respiration.

4(b)(ii)Aerobic Anaerobic RespirationEasy2 marks

Explain why the rate of aerobic respiration increases at the start of the race.

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4(b)(iii)Aerobic Anaerobic RespirationEasy1 mark

State where aerobic respiration occurs in cells.

4(c)Aerobic Anaerobic RespirationHard4 marks

Explain why the heart rate does not immediately return to its resting value after the race ends in Figure 4.1.

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4(d)Hormones Endocrine SystemEasy2 marks

Adrenaline is also released during the race and increases heart rate. Describe two other effects of adrenaline that enable efficient respiration.

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4(e)Heart CirculationEasy2 marks

Blood is transported to the heart in veins. Explain the structural adaptations of veins.

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