AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
During exercise the human body reacts to the increased demand for energy.
Full specification wording
Response to exercise: During exercise the human body reacts to the increased demand for energy.
Exercise increases the rate of respiration in muscle cells because more energy is needed for muscle contraction.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 1 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Exercise increases the rate of respiration in muscle cells because more energy is needed for muscle contraction. The body responds to this increased demand in several coordinated ways. Heart rate and breathing rate increase, and breathing becomes deeper, so more oxygen enters the blood and more carbon dioxide is removed. Blood vessels supplying muscles widen, increasing blood flow and glucose delivery, while other vessels may narrow. Glycogen stores in muscles are broken down to glucose for respiration. If oxygen supply cannot keep pace, anaerobic respiration supplements aerobic respiration and lactic acid builds up, causing muscle fatigue. After exercise, breathing and heart rate remain elevated to repay the oxygen debt and remove lactic acid.
What earns the marks
- Exercise increases the demand for energy in muscle cells.
- Heart rate and breathing rate increase during exercise.
- Breathing becomes deeper, increasing oxygen uptake and carbon dioxide removal.
- Blood flow to muscles increases through widening of blood vessels supplying muscles.
- Glycogen in muscles is converted to glucose for respiration.
- If oxygen supply is insufficient, anaerobic respiration occurs and lactic acid builds up.
- After exercise, increased breathing and heart rate help repay the oxygen debt and remove lactic acid.
Common mistakes and how to put them right
Saying the body stops respiring anaerobically as soon as exercise begins.
Put it right by stating that anaerobic respiration supplements aerobic respiration when oxygen supply is insufficient.
Confusing oxygen debt with a lack of oxygen in the lungs.
Put it right by describing oxygen debt as the extra oxygen needed after exercise to remove lactic acid.
Thinking only heart rate changes during exercise.
Put it right by including increased breathing rate and depth, and increased blood flow to muscles.
Exam tips
- Link each body response to its purpose, such as increased heart rate delivering more oxygen and glucose to muscles.
- Use the term oxygen debt when explaining why breathing and heart rate stay high after exercise.
- Describe changes in both rate and depth of breathing, and in blood flow to muscles, to show a full response.
Try the lesson
The start of the Response to exercise: During exercise the human body reacts to the increased demand for energy. lesson, made from checked teaching notes for this specification point.
Have a go first
How does the human body's breathing rate change in response to the increased demand for energy during exercise?
Listen
Exercise increases the rate of respiration in muscle cells because more energy is needed for muscle contraction. The body responds to this increased demand in several coordinated ways. Heart rate and breathing rate increase, and breathing becomes deeper, so more oxygen enters the blood and more carbon dioxide is removed. Blood vessels supplying muscles widen, increasing blood flow and glucose delivery, while other vessels may narrow. Glycogen stores in muscles are broken down to glucose for respiration. If oxygen supply cannot keep pace, anaerobic respiration supplements aerobic respiration and lactic acid builds up, causing muscle fatigue. After exercise, breathing and heart rate remain elevated to repay the oxygen debt and remove lactic acid. A strong answer earns marks for these points. Exercise increases the demand for energy in muscle cells. Heart rate and breathing rate increase during exercise. Breathing becomes deeper, increasing oxygen uptake and carbon dioxide removal. Blood flow to muscles increases through widening of blood vessels supplying muscles. A common slip: Saying the body stops respiring anaerobically as soon as exercise begins. Instead, stating that anaerobic respiration supplements aerobic respiration when oxygen supply is insufficient. Exam tip: Link each body response to its purpose, such as increased heart rate delivering more oxygen and glucose to muscles.
Key words
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oxygen debt
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anaerobic respiration
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lactic acid
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glycogen
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See every definition
- oxygen debt
- The extra oxygen needed after exercise to remove lactic acid.
- anaerobic respiration
- Respiration that supplements aerobic respiration when oxygen supply is insufficient, causing lactic acid to build up.
- lactic acid
- A substance that builds up when anaerobic respiration occurs, causing muscle fatigue.
- glycogen
- Stores in muscles that are broken down to glucose for respiration.
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