AQA GCSE Combined Science Foundation (8464), Foundation tier · Biology › Bioenergetics › Respiration
Practise Response to exercise. 6 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
How your body meets the extra energy demand of exercise: heart rate, breathing rate and breath volume increase, and if the muscles run short of oxygen they respire anaerobically, causing lactic acid to build up and muscle fatigue. Expect data on heart rate or breathing, often with a calculation.
Key facts
Exercise → heart rate, breathing rate and breath volume increase
Purpose: more oxygenated blood to the muscles for respiration
Not enough oxygen → anaerobic respiration: glucose → lactic acid
Long vigorous exercise → muscles fatigue and stop contracting efficiently
Percentage change = (new − original) ÷ original × 100
Notes
Changes during exercise
During exercise your muscles contract more, so they need more energy from respiration.
Your heart rate, breathing rate and breath volume (how much air each breath moves) all increase.
This supplies the muscles with more oxygenated blood, bringing more oxygen and glucose for aerobic respiration and removing the extra carbon dioxide.
When oxygen runs short
In vigorous exercise the heart and lungs cannot supply oxygen fast enough, so muscle cells also respire anaerobically: glucose → lactic acid.
The oxidation of glucose is incomplete, so lactic acid builds up in the muscles.
During long periods of vigorous activity, muscles become fatigued and stop contracting efficiently.
Anaerobic respiration adds to aerobic respiration; it does not replace it.
Working with exercise data
diagram
Heart rate is measured in beats per minute: count your pulse for 15 seconds and multiply by 4.
Breathing rate is measured in breaths per minute.
Percentage increase = (value during exercise − resting value) ÷ resting value × 100.
Recovery time is how long the rate takes to return to its resting value after exercise. A fitter person usually has a lower resting heart rate and recovers more quickly.
Heart rate stays high for a while after exercise stops. A fitter person recovers sooner.
How to answer each type of question
Explain why heart rate and breathing rate increase
2 to 3 marksGrade 5
Start with the muscles: they contract more, so they need more energy.
Say that more respiration is needed.
Link the changes to supplying more oxygen (and glucose) in the blood, and removing carbon dioxide.
Example. During a race a runner's heart rate and breathing rate increase. Explain why.
Show the model answerHide the model answer
The muscles are contracting more, so they need more energy (1). This energy comes from more (aerobic) respiration (1). So more oxygenated blood must be pumped to the muscles, to supply more oxygen (and glucose) (1).
Calculate a percentage change from exercise data
2 marksGrade 5
Find the change: new value − original (resting) value.
Divide by the original value, not the new one.
Multiply by 100 and add the % sign.
Example. A student's resting heart rate was 64 beats per minute. After 3 minutes of running it was 112 beats per minute. Calculate the percentage increase in heart rate.
Show the model answerHide the model answer
112 − 64 = 48 (1) 48 ÷ 64 × 100 = 75% (1)
Don’t lose marks
Saying you breathe faster 'to get more energy'. Breathing supplies oxygen; respiration transfers the energy.
Saying 'the heart pumps oxygen to the muscles'. The heart pumps oxygenated blood.
Saying muscles switch from aerobic to anaerobic respiration. In hard exercise they respire aerobically and anaerobically at the same time.
In percentage change questions, dividing by the value during exercise instead of the resting value.
More tips
Memory tricks
Three things go up: heart rate, breathing rate and breath volume.
Fatigue chain: not enough oxygen → anaerobic respiration → lactic acid builds up → fatigue.
Exam technique
Link every change to its purpose: heart rate increases → more oxygenated blood to the muscles → more aerobic respiration.
When you describe data, quote figures with units, for example 'rose from 70 to 150 beats per minute'.
Treat breathing rate and breath volume as two separate changes; each can be a separate mark.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
State how exercise changes heart and breathingHeart rate, breathing rate and breath volume all increase.
Grade 4
Explain why heart and breathing rates increaseTo supply the muscles with more oxygenated blood for the extra respiration needed to contract.
Grade 5
Explain when muscles respire anaerobicallyWhen oxygen cannot be supplied fast enough for aerobic respiration alone, as in vigorous exercise.
Grade 5
Calculate changes from exercise dataWork out increases, percentage changes and recovery times from tables and graphs of heart rate or breathing rate.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Which substance builds up in the muscles during vigorous exercise if not enough oxygen is supplied?
Lactic acid
Name the substance that builds up in muscles during vigorous exercise, if they respire anaerobically.
Lactic acid
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy6 marks
During exercise the body needs to transfer more energy.
(a) Which three changes happen in the body during exercise? Tick (✓) three boxes.[3]
Breathing rate increases
Breath volume increases
Heart rate decreases
Heart rate increases
Body temperature falls
(b) Explain why these changes are needed during exercise.[2]
(c) Which substance builds up in the muscles during vigorous exercise if not enough oxygen is supplied?[1]
to supply the muscles with more oxygenated blood / more oxygen (and glucose)
for faster (aerobic) respiration, to transfer more energy for muscle contraction
to remove more carbon dioxide
(c)Answer: Lactic acid
lactic acid
Question 2Medium5 marks
At high altitude, the concentration of oxygen in the air is lower than at sea level. Athletes training at high altitude often notice their heart rate and breathing rate are higher than usual for the same amount of exercise.
(a) Explain why breathing rate and heart rate are higher than usual for the same exercise at high altitude.[2]
(b) Explain why an athlete’s muscles might rely more on anaerobic respiration during exercise at high altitude than at sea level.[2]
(c) Suggest one reason why athletes who train at high altitude for several weeks may then perform better at sea level.[1]
Show the answer and mark scheme
(a)
less oxygen is available in each breath of air
the body increases breathing rate and heart rate to try to take in and deliver enough oxygen to the muscles
(b)
even with faster breathing and heart rate, less oxygen reaches the muscles than at sea level
if the muscles cannot get enough oxygen for aerobic respiration alone, they respire anaerobically as well
(c)
the body may adapt by producing more red blood cells / more haemoglobin, so the blood can carry more oxygen to the muscles
the heart and the breathing muscles may become stronger, so more oxygen is delivered to the muscles