AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Oxygen debt is the amount of extra oxygen the body needs after exercise to…
Full specification wording
Response to exercise: Oxygen debt is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells.
When muscles respire anaerobically during intense exercise, lactic acid builds up.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 7 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
When muscles respire anaerobically during intense exercise, lactic acid builds up. After exercise, the body continues to breathe rapidly and deeply. This extra oxygen is needed to repay the oxygen debt. This specific statement is Higher Tier only content: oxygen debt is defined as the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells. Blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose. Oxygen debt explains why recovery takes time and why breathing and heart rate remain elevated after exercise stops. It links anaerobic respiration, lactic acid, and liver function.
What earns the marks
- State that oxygen debt is the extra oxygen required after exercise to react with accumulated lactic acid (Higher Tier only).
- Explain that lactic acid accumulates in muscles during anaerobic respiration.
- Describe how blood transports lactic acid from the muscles to the liver (Higher Tier only).
- Explain that in the liver, lactic acid is converted back into glucose, which requires oxygen (Higher Tier only).
- Note that breathing rate and heart rate stay high after exercise to deliver the extra oxygen and remove carbon dioxide.
Common mistakes and how to put them right
Defining oxygen debt as the oxygen used during exercise.
Put it right by stating it is the extra oxygen needed after exercise to deal with accumulated lactic acid.
Saying lactic acid is removed by breathing it out.
Put it right by explaining that lactic acid is transported to the liver and converted back into glucose (Higher Tier), while carbon dioxide is exhaled.
Thinking oxygen debt disappears immediately when exercise stops.
Put it right by linking the debt to the time needed for the liver to process lactic acid, during which breathing and heart rate remain elevated.
Exam tips
- Remember to specify that lactic acid is transported to the liver for conversion back to glucose (Higher Tier).
- If a graph of breathing rate is given, identify the period after exercise where the rate is still above resting level as the time when oxygen debt is being repaid.
Try the lesson
The start of the Response to exercise: Oxygen debt is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells. lesson, made from checked teaching notes for this specification point.
Have a go first
In the context of respiration and exercise, what is the correct biological definition of oxygen debt?
Listen
When muscles respire anaerobically during intense exercise, lactic acid builds up. After exercise, the body continues to breathe rapidly and deeply. This extra oxygen is needed to repay the oxygen debt. This specific statement is Higher Tier only content: oxygen debt is defined as the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells. Blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose. Oxygen debt explains why recovery takes time and why breathing and heart rate remain elevated after exercise stops. It links anaerobic respiration, lactic acid, and liver function. A strong answer earns marks for these points. State that oxygen debt is the extra oxygen required after exercise to react with accumulated lactic acid (Higher Tier only). Explain that lactic acid accumulates in muscles during anaerobic respiration. Describe how blood transports lactic acid from the muscles to the liver (Higher Tier only). Explain that in the liver, lactic acid is converted back into glucose, which requires oxygen (Higher Tier only). A common slip: Defining oxygen debt as the oxygen used during exercise. Instead, stating it is the extra oxygen needed after exercise to deal with accumulated lactic acid. Exam tip: Remember to specify that lactic acid is transported to the liver for conversion back to glucose (Higher Tier).
Key words
Say what each word means before you turn the card.
Oxygen debt
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Lactic acid
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Liver
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Glucose
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See every definition
- Oxygen debt
- The amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells.
- Lactic acid
- A substance that builds up when muscles respire anaerobically during intense exercise and accumulates in muscles.
- Liver
- The organ to which blood transports lactic acid, where it is converted back into glucose.
- Glucose
- What lactic acid is converted back into in the liver, which requires oxygen.
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