Figure 8 shows the heart rate of person A and person B - Edexcel - GCSE Biology Combined Science - Question 5 - 2020 - Paper 1

Cardiac output (CO) can be calculated using the formula: $CO = ext{Stroke Volume} imes ext{Heart Rate}$

Assuming the heart rate for person B before exercising was around 70 bpm, we can substitute: $CO = 61 ext{ ml} imes 70 ext{ bpm}$ This gives: $CO = 4270 ext{ ml/min} = 4.27 ext{ litres/min}$

Person A needed a higher heart rate during exercise because their body is less efficient at delivering oxygen and nutrients to the tissues due to lack of conditioning. To compensate for this inefficiency, the heart must pump faster to achieve a sufficient cardiac output. In contrast, person B, being more fit, can maintain adequate blood flow with a lower heart rate, making their cardiovascular system more efficient.