AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Response to exercise: (HT only) Blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose. 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.
After anaerobic respiration in muscles, lactic acid must be removed to prevent lasting harm.
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
After anaerobic respiration in muscles, lactic acid must be removed to prevent lasting harm. Blood flowing through the muscles carries lactic acid to the liver, where it is converted back into glucose. This process requires oxygen, so the body continues to breathe deeply after exercise. The 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. For example, after a 400 m race, a runner keeps panting; the extra oxygen helps the liver convert lactic acid back to glucose. This entire clause is Higher Tier (HT) only; Foundation Tier students are not assessed on oxygen debt or lactic acid conversion.
What earns the marks
- (HT only) Blood flowing through the muscles transports lactic acid away from the muscle cells.
- (HT only) The liver is the organ where lactic acid is converted back into glucose.
- (HT only) The conversion of lactic acid back to glucose in the liver requires oxygen.
- (HT only) Oxygen debt is the extra oxygen needed after exercise to react with accumulated lactic acid.
- (HT only) Removing lactic acid from the cells prevents it from continuing to cause fatigue and allows recovery.
Common mistakes and how to put them right
Stating that lactic acid is converted into glucose in the muscles.
Put it right: The conversion happens in the liver after blood transports lactic acid there (HT only).
Defining oxygen debt as the oxygen used during exercise.
Put it right: It is the extra oxygen needed after exercise to react with accumulated lactic acid and remove it (HT only).
Saying lactic acid is excreted unchanged in urine.
Put it right: It is converted back into glucose in the liver, which requires oxygen (HT only).
Exam tips
- Name the liver as the site of conversion and state that blood transports lactic acid there (HT only).
- Use the definition of oxygen debt precisely: extra oxygen needed after exercise to react with accumulated lactic acid and remove it from the cells (HT only).
Try the lesson
The start of the Response to exercise: (HT only) Blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose. 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
Which organ converts lactic acid back into glucose after exercise?
Listen
After anaerobic respiration in muscles, lactic acid must be removed to prevent lasting harm. Blood flowing through the muscles carries lactic acid to the liver, where it is converted back into glucose. This process requires oxygen, so the body continues to breathe deeply after exercise. The 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. For example, after a 400 m race, a runner keeps panting; the extra oxygen helps the liver convert lactic acid back to glucose. This entire clause is Higher Tier (HT) only; Foundation Tier students are not assessed on oxygen debt or lactic acid conversion. A strong answer earns marks for these points. HT only) Blood flowing through the muscles transports lactic acid away from the muscle cells. HT only) The liver is the organ where lactic acid is converted back into glucose. HT only) The conversion of lactic acid back to glucose in the liver requires oxygen. HT only) Oxygen debt is the extra oxygen needed after exercise to react with accumulated lactic acid. A common slip: Stating that lactic acid is converted into glucose in the muscles. Instead, the conversion happens in the liver after blood transports lactic acid there (HT only). Exam tip: Name the liver as the site of conversion and state that blood transports lactic acid there (HT only).
Key words
Say what each word means before you turn the card.
Oxygen debt
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Liver
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Lactic acid
Try answering aloud or in your head before turning the card.
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.
- Liver
- The organ where lactic acid is converted back into glucose, which requires oxygen.
- Lactic acid
- Carried by blood flowing through the muscles to the liver, where it is converted back into glucose.
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Test your understanding of Response to exercise: (HT only) Blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose. 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.
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