AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
The incomplete oxidation of glucose causes a build up of lactic acid and…
Full specification wording
Response to exercise: The incomplete oxidation of glucose causes a build up of lactic acid and creates an oxygen debt.
When oxygen is insufficient, glucose is not completely oxidised to carbon dioxide and water.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 4 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
When oxygen is insufficient, glucose is not completely oxidised to carbon dioxide and water. Instead, partial breakdown produces lactic acid, which accumulates in muscle cells and then diffuses into the blood. This accumulation is described as an oxygen debt: the extra oxygen that must eventually be taken in to oxidise the lactic acid. After exercise, lactic acid is transported to the liver, where it is converted back to glucose, a process that requires oxygen. The debt is repaid by continued fast breathing and a raised heart rate after exercise stops.
For example: A runner continues to breathe heavily for several minutes after a race while lactic acid is removed.
What earns the marks
- State that incomplete oxidation of glucose in muscles produces lactic acid.
- Explain that lactic acid accumulates in muscles and blood during vigorous exercise.
- Define oxygen debt as the extra oxygen needed after exercise to remove or oxidise lactic acid.
- Describe how lactic acid is transported to the liver and converted back to glucose, requiring oxygen.
Common mistakes and how to put them right
Saying oxygen debt is the oxygen breathed in during exercise.
Put it right: Oxygen debt is the extra oxygen required after exercise to deal with lactic acid.
Saying lactic acid is converted to carbon dioxide in the liver.
Put it right: Lactic acid is converted back to glucose in the liver.
Saying lactic acid builds up because glucose is completely oxidised.
Put it right: Incomplete oxidation of glucose produces lactic acid.
Exam tips
- Define oxygen debt in one sentence, then explain how continued fast breathing and raised heart rate repay it.
- Link lactic acid removal to the liver and to the oxygen required for conversion back to glucose.
- Use the term incomplete oxidation to show why lactic acid, rather than carbon dioxide and water, is formed.
Try the lesson
The start of the Response to exercise: The incomplete oxidation of glucose causes a build up of lactic acid and creates an oxygen debt. lesson, made from checked teaching notes for this specification point.
Have a go first
Which substance builds up in muscles when glucose is broken down without enough oxygen during vigorous exercise?
Listen
When oxygen is insufficient, glucose is not completely oxidised to carbon dioxide and water. Instead, partial breakdown produces lactic acid, which accumulates in muscle cells and then diffuses into the blood. This accumulation is described as an oxygen debt: the extra oxygen that must eventually be taken in to oxidise the lactic acid. After exercise, lactic acid is transported to the liver, where it is converted back to glucose, a process that requires oxygen. The debt is repaid by continued fast breathing and a raised heart rate after exercise stops. For example, a runner continues to breathe heavily for several minutes after a race while lactic acid is removed. A strong answer earns marks for these points. State that incomplete oxidation of glucose in muscles produces lactic acid. Explain that lactic acid accumulates in muscles and blood during vigorous exercise. Define oxygen debt as the extra oxygen needed after exercise to remove or oxidise lactic acid. Describe how lactic acid is transported to the liver and converted back to glucose, requiring oxygen. A common slip: Saying oxygen debt is the oxygen breathed in during exercise: the error is placing the debt during activity. Instead, oxygen debt is the extra oxygen required after exercise to deal with lactic acid. Exam tip: Define oxygen debt in one sentence, then explain how continued fast breathing and raised heart rate repay it.
Key words
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Incomplete oxidation of glucose
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Oxygen debt
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Lactic acid accumulation and removal
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Liver function in metabolism
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See every definition
- Incomplete oxidation of glucose
- When oxygen is insufficient, glucose is not completely oxidised to carbon dioxide and water, and partial breakdown produces lactic acid.
- Oxygen debt
- The extra oxygen that must eventually be taken in to oxidise the lactic acid, repaid by continued fast breathing and a raised heart rate after exercise stops.
- Lactic acid accumulation and removal
- Lactic acid accumulates in muscle cells and diffuses into the blood, then is transported to the liver where it is converted back to glucose.
- Liver function in metabolism
- The liver converts lactic acid back to glucose, a process that requires oxygen.
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