Response to Exercise
Get to grips with Response to Exercise for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Understand oxygen debt, and how heart rate, breathing rate and breath volume all increase during exercise.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
During exercise the body needs more energy, so the rate of respiration increases. Several responses occur to supply the muscles with more oxygen and glucose.
Heart rate, breathing rate and breath depth all increase. Together these deliver more oxygenated blood to the muscles and remove carbon dioxide faster. Glycogen stored in the muscles is converted back to glucose to fuel respiration.
If insufficient oxygen reaches the muscles, anaerobic respiration occurs and lactic acid builds up, causing muscle fatigue. The oxygen debt is the amount of extra oxygen the body needs afterwards to react with and remove that lactic acid, which is why breathing stays elevated after exercise stops.
Revision notes
Responses to exercise
Heart rate increases, breathing rate increases and the depth of each breath increases.
These supply the muscles with more oxygen and glucose for respiration, and remove carbon dioxide more quickly. Glycogen stores in the muscles are converted back to glucose.
Oxygen debt
If muscles respire anaerobically, lactic acid builds up and causes fatigue so the muscles stop contracting efficiently.
The oxygen debt is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it. This is why you continue breathing heavily after stopping.
Removing lactic acid
Blood flowing through the muscles transports lactic acid to the liver.
In the liver it is converted back into glucose. Until this is complete, breathing and heart rate remain above resting levels.
Key points
- Exercise increases heart rate, breathing rate and breath depth.
- These supply more oxygen and glucose to the muscles.
- Glycogen in muscles is converted back to glucose.
- Insufficient oxygen leads to anaerobic respiration.
- Lactic acid causes muscle fatigue.
- Oxygen debt is the extra oxygen needed to remove lactic acid.
Worked examples
Example 1
Describe three ways the body responds to an increased demand for energy during exercise. [3 marks]
Model answer
Heart rate increases (1 mark), breathing rate increases (1 mark), and the depth of each breath increases (1 mark).
Example 2
Explain what is meant by oxygen debt. [2 marks]
Model answer
The oxygen debt is the amount of extra oxygen the body needs after exercise (1 mark) to react with and remove the lactic acid that has built up during anaerobic respiration (1 mark).
Example 3
Explain why a person continues to breathe heavily for several minutes after stopping exercise. [3 marks]
Model answer
Lactic acid has built up in the muscles from anaerobic respiration (1 mark). Extra oxygen is needed to break this down (1 mark), so breathing remains rapid and deep until the oxygen debt has been repaid (1 mark).
Common mistakes
Saying lactic acid is removed by breathing it out.
It is transported in the blood to the liver and converted back to glucose.
Confusing glycogen with glucagon.
Glycogen is the storage carbohydrate; glucagon is a hormone.
Saying oxygen debt is a lack of oxygen during exercise.
It is the extra oxygen required afterwards to remove lactic acid.
Giving only heart rate as a response.
Breathing rate and breath depth also increase.
Exam tips
- Give all three responses when the marks allow.
- Define oxygen debt as extra oxygen needed afterwards.
- Name the liver as where lactic acid is converted.
- Keep glycogen and glucagon clearly separate.
Key terms
- Glycogen
- The storage carbohydrate in muscles and liver.
- Oxygen debt
- The extra oxygen needed after exercise to remove lactic acid.
- Muscle fatigue
- The point at which muscles stop contracting efficiently.
- Lactic acid
- The product of anaerobic respiration in muscle.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.