Learning focus
Build precise biological explanations, interpret diagrams and data, and connect structure, process, health and practical evidence.
Pulse rate
A pulse is the pressure wave produced when the ventricles eject blood into arteries. It can be felt where an artery passes near the skin over a firm structure, such as at the wrist. Pulse rate normally corresponds to heart rate, although some abnormal beats may not produce an effective pulse.
Heart sounds
Listening with a stethoscope detects sounds caused mainly by valves closing. Rate and regularity can be assessed. A stethoscope does not directly record electrical activity or blood pressure.
Electrocardiogram
An ECG records changing electrical potential at the skin caused by electrical activity in the heart. Each normal cycle has a repeating pattern associated with atrial and ventricular activation and recovery. At O Level, candidates need to know that ECG can monitor heart activity, not detailed wave names.
Measurement reliability
Measure pulse for a known time, preferably 30 or 60 seconds, while the subject is resting. Short counts multiplied to a minute increase percentage uncertainty. Repeat measurements, use the same posture and allow recovery between exercise trials.
Interpreting data
Heart rate varies naturally between individuals and with fitness, emotion, temperature and recent activity. A single value cannot diagnose disease. In experiments, compare the same participant before and after a controlled activity or use a sufficiently large sample.
Practical or data skill
Measure resting pulse three times, calculate a mean, then repeat immediately after standardised exercise and during recovery. Plot heart rate against time and identify the recovery pattern.
Examination tip
State exactly how pulse is measured and converted to beats per minute; do not merely say “use a stopwatch”.
Review questions and suggested answers
Question 1
What does an ECG record?
Suggested answer
Electrical activity of the heart.
Question 2
Why is counting for 60 seconds more precise than 10 seconds?
Suggested answer
It reduces the effect of one-beat counting error and avoids multiplying a short count by a large factor.
Question 3
What produces the arterial pulse?
Suggested answer
Pressure waves caused by ventricular contraction and blood ejection.
