Anaerobic respiration
Laura Armstrong & Joe Wolfensohn
Teachers
Contents
Recall Questions
This topic requires prior knowledge of aerobic respiration.
What gas is needed for aerobic respiration?
Oxygen.
What are the products of aerobic respiration?
Carbon dioxide and water.
Where in the cell does aerobic respiration happen?
In the mitochondria.
Topic Explainer Video
Check out this @JoeDoesBiology video that explains anaerobic respiration, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
What is Anaerobic Respiration?
Anaerobic respiration is a chemical reaction that releases energy from glucose without oxygen. It happens when not enough oxygen is available, such as during intense exercise. It takes place in the cytoplasm of cells.
Word Equations
In animals:
Glucose → lactic acid (+energy)
In plants and yeast (fermentation):
Glucose → ethanol + carbon dioxide (+energy)
You do not need to learn the symbol equations for these reactions!
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When Does Anaerobic Respiration Occur?
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In muscle cells during vigorous exercise when oxygen can’t be delivered fast enough to the cells.
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In plants and yeast cells (when oxygen is limited).
In Animals Anaerobic Respiration Leads to Lactic Acid and Oxygen Debt
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Lactic acid builds up and causes muscle fatigue and cramps.
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After exercise, oxygen is needed to break down lactic acid – this is called repaying the oxygen debt.
In Yeast anaerobic respiration (fermentation) has economic importance
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Yeast is used in bread making as the bubbles of carbon dioxide produced during anaerobic respiration help bread to rise.
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Yeast is used in the manufacture of alcoholic drinks as ethanol (alcohol) is produced during anaerobic respiration.
Higher tier only
The lactic acid travels in the bloodstream to the liver where it is oxidised (broken down using oxygen) and converted back into glucose.
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This is why you continue to breathe heavily after stopping exercise- to provide the extra oxygen needed to break down the lactic acid.
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Your heart rate also remains higher after exercise to deliver oxygen more quickly to cells.
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Aerobic vs Anaerobic Respiration
|
Feature |
Aerobic Respiration |
Anaerobic Respiration |
|
Oxygen needed? |
Yes |
No |
|
Glucose breakdown |
Complete |
Incomplete |
|
Products in animals |
CO₂ + H₂O |
Lactic acid |
|
Products in plants/ yeast |
CO₂ + H₂O |
Ethanol + CO₂ |
|
Energy released |
Large amount |
Small amount |
|
Energy released |
Slowly |
Quickly |
|
Where? |
Mitochondria |
Cytoplasm |
Make sure you learn the following equations -
Key Terms
- Anaerobic respiration - Respiration without oxygen.
- Lactic acid - Waste product made in anaerobic respiration in animals.
- Fermentation - Anaerobic respiration in yeast and plants producing ethanol and CO₂.
- Oxygen debt - Extra oxygen needed to break down lactic acid after exercise.
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Exam Tip
Be careful not to confuse anaerobic respiration in yeast and plants with anaerobic respiration in humans – the products are different!
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Practice Question
Compare the processes of aerobic and anaerobic respiration in humans. (4 marks)
Any 4 from-
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Aerobic respiration uses oxygen, anaerobic does not (1).
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Aerobic respiration produces carbon dioxide and water, anaerobic produces lactic acid (1).
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Aerobic releases more energy, anaerobic releases less energy (1).
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Both processes use glucose and release energy (1).
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Anaerobic respiration leads to an oxygen debt, this does not happen in aerobic respiration (1).
More Practice
Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!