IGCSE Biology Practical Skills 9: Heart Rate and Breathing Rate

Heart rate and breathing rate are explicit Cambridge IGCSE Biology practical contexts. Topic 11 also requires investigation of physical activity effects on breathing rate and depth and comparison of inspired and expired air using limewater. Human investigations need reproducible timing, controlled activity, participant welfare and appropriately limited conclusions.

Define the measured outcome

Heart rate is beats per minute. Pulse rate is commonly used as a proxy because each heartbeat normally produces a pressure pulse in an artery.

Breathing rate is breaths per minute. Breathing depth describes the volume moved per breath, not how forcefully a participant appears to breathe. Direct depth measurement needs suitable apparatus; chest movement or another supplied measure is only a proxy.

Ventilation rate combines rate and volume per breath. Do not call breathing rate alone ventilation volume.

Recovery time is the time taken for a response to return to a defined baseline or threshold. State the criterion before analysing data.

Establish a baseline

Ask the participant to sit quietly in the same posture for a standard rest period. Measure resting pulse and breathing rate more than once until readings are reasonably stable.

Use the same counting interval for every measurement. A full minute reduces multiplication and short-interval fluctuation, while a shorter interval may be necessary immediately after exercise. If counting for 15 or 30 seconds, convert correctly to a per-minute rate.

Record room temperature, recent activity and time of measurement where relevant. An unstable baseline weakens every comparison that follows.

Measure pulse consistently

Locate a pulse at the wrist or another instructed safe site using fingertips rather than a thumb, which has its own detectable pulse. Count beats for the defined interval.

An electronic heart-rate sensor can reduce counting burden and provide continuous recovery data, but check placement and recording interval. It does not remove biological variation or the need for a stable baseline.

Manual counting can miss beats at high rates. Two observers should not press simultaneously on different sites in a way that changes the method. Use one standard protocol.

Measure breathing rate and depth

Count one complete inhale-exhale cycle as one breath. Observe discreetly because conscious attention can change breathing.

Use the same posture and interval. If breathing depth is required, use supplied spirometry, chest displacement or another defined method. A larger chest movement may indicate greater depth but is not automatically an exact volume.