Learning focus
Build precise biological explanations, interpret diagrams and data, and connect structure, process and practical evidence.
Increased demand
During exercise, muscles contract more frequently and require more energy. Aerobic respiration rate rises, increasing oxygen demand and carbon dioxide production. Breathing becomes faster and deeper to increase ventilation.
Rate and depth
Breathing rate is breaths per minute. Breathing depth is the volume of air moved per breath. Both can rise, so minute ventilation increases more than either alone. A complete answer mentions both when the question asks about breathing response.
Recovery
After exercise, breathing remains elevated while carbon dioxide is removed, oxygen stores are restored and any lactic acid is processed. The recovery time depends on exercise intensity and fitness.
Investigation
Measure resting breathing for a fixed time, perform standardised exercise, then measure immediately and at regular intervals. Control exercise duration and intensity, posture and counting period. Use several participants or repeats and calculate means.
Data interpretation
Identify resting value, peak value, recovery trend and anomalies. Correlation does not by itself prove a mechanism, so combine graph description with physiological explanation. Avoid judging fitness from a single measurement without controls.
Practical or data skill
Plan a step-test investigation comparing breathing rate before and after a fixed exercise. Include safety screening, a stop rule, standardised pace, rest between repeats and no competition beyond safe limits.
Examination tip
Exercise increases both breathing rate and breathing depth to supply more oxygen and remove more carbon dioxide.
Review questions and suggested answers
Question 1
Why does breathing depth increase during exercise?
Suggested answer
To move more air per breath, increasing oxygen supply and carbon dioxide removal.
Question 2
Why does breathing remain high after exercise?
Suggested answer
To support recovery, including removal and breakdown of lactic acid and restoration of normal conditions.
Question 3
Name one control variable in an exercise investigation.
Suggested answer
Exercise duration, pace, step height, participant, posture or counting interval.
