Two dancers each perform the same five-minute routine. A pulse oximeter records Dancer P's heart rate 15 seconds after the routine and Dancer Q's heart rate 90 seconds after the routine.
Dancer P's recorded heart rate is 154 bpm and Dancer Q's recorded heart rate is 138 bpm.
A teacher concludes that Dancer P had a higher heart rate than Dancer Q when the routine ended.
Why is this conclusion not supported by the results?
The dancers may have different resting heart rates, so their heart rates after exercise cannot be compared.
Dancer Q had recovered for longer, so their heart rate may have fallen further before measurement.
Dancer P was measured sooner, so their heart rate had less time to rise to its highest value.
A pulse oximeter measures stroke volume, so its readings do not show either dancer's heart rate.
67 exam-style questions on Edexcel GCSE Biology 8.2 Blood and circulation, covering 8.2.1 Structure and function of the blood, 8.2.2 Structure of blood vessels, 8.2.3 Structure of the heart and circulatory system, and 8.2.4 Cardiac output. Each one has a worked solution and a mark scheme showing where the marks go.