Pulse rate before and after exercise is the heart-rate practical that IGCSE Biology Paper 5 and Paper 6 keep setting, and every mark is in the technique: a settled subject, a fair count, the conversion to beats per minute, the anomaly, the bar chart. By hand, carry your fingers to the subject’s wrist, run the counting stopwatch for 15 seconds while tapping the tally counter for every beat you feel, and do it three times. Press and hold the step for a minute of step-ups, then count straight away and every minute after as the pulse comes down (the speed lever skips the waiting, but you can only count at normal speed). Then the table, the means, a bar chart you draw by dragging the bars, a percentage increase and the biology of the oxygen debt. Every attempt uses a different subject. Allow about 30 minutes.
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Headings with the quantity and its unit, three separate 15-second counts that match the beats while your fingers were on the wrist (within 2), every pulse rate = count × 4, the anomalous trial picked out by comparing it with the other two (counting before the subject has settled gives one), and the mean of the reliable values. Examiner reports on 0610 practical papers note that candidates forget the conversion from 15 seconds to a minute.
A full minute of step-ups timed on stopwatch 1, then five 15-second counts each started within 10 seconds of the stated time after the exercise, each within 2 beats of the pulse at that moment, all converted to beats per minute.
A y-axis scale that fits the highest value and uses more than half of the grid, every bar within half a small square of your own table value, and the percentage increase = (after − rest) ÷ rest × 100 to 2 significant figures.
Pulse rises because respiring muscles need more oxygen and glucose and produce more carbon dioxide; it stays high afterwards while the oxygen debt from anaerobic respiration (lactic acid) is repaid.
Two things kept the same (the subject, the 15-second count, the exercise), the main source of error (missed or double-counted beats, multiplied by four), an improvement that really adds reliability (longer counts, repeats and a mean, a pulse sensor) and a safety precaution tied to the exercise.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.