Comparing aerobic and anaerobic respiration

Exchange and transport in animals · Respiration · note 2 of 3

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Comparing aerobic and anaerobic respirationSpec 8.10

In short

Aerobic respiration needs oxygen and completely breaks down glucose, releasing a large amount of energy per glucose molecule. Anaerobic respiration does not need oxygen and only partly breaks down glucose, so it releases much less energy. Both are exothermic. Anaerobic respiration happens when oxygen is not available, for example in muscles during vigorous exercise.

Aerobic and anaerobic respiration compared
	Aerobic respiration	Anaerobic respiration
Oxygen needed?	Yes	No
Glucose breakdown	Complete breakdown	Incomplete breakdown
Energy released	A large amount per glucose molecule	Much less per glucose molecule
Products in animals	Carbon dioxide and water	Lactic acid
Products in plants and yeast	Carbon dioxide and water	Ethanol and carbon dioxide
When it happens	Whenever enough oxygen is available	When oxygen is not available, for example in muscles during vigorous exercise

Aerobic respiration releases much more energy because glucose is completely broken down. Anaerobic respiration releases less energy because glucose is only partly broken down. Both types of respiration are exothermic and both release energy from glucose.

Exam tip:

A comparison needs both sides in the same sentence, for example: aerobic respiration releases more energy per glucose than anaerobic respiration.

Written and checked against the Edexcel GCSE Combined Science (1SC0) specification · Updated October 2026

Frequently asked questions

Why is respiration an exothermic reaction?

Respiration is exothermic because it transfers energy to the surroundings, and some of this energy is released as heat. It happens continuously in the living cells of plants and animals to release energy for metabolic processes, such as building larger molecules, muscle contraction and keeping mammals and birds warm. Aerobic and anaerobic respiration are both exothermic.

How is respiration different from breathing?

Respiration is a chemical reaction in cells that releases energy from glucose, while breathing is the movement of air into and out of the lungs. Respiration happens continuously in all living cells, in plants as well as animals. It is also not the same as gas exchange, which is the diffusion of gases between the alveoli and the blood.

What is the difference between aerobic and anaerobic respiration?

Aerobic respiration uses oxygen and completely breaks down glucose to carbon dioxide and water, releasing a large amount of energy. Anaerobic respiration happens without oxygen and breaks glucose down only partly, so it releases much less energy. In animals it produces lactic acid, and in plants and yeast it produces ethanol and carbon dioxide.

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