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Respiration is a chemical reaction that happens in all living cells, including plant cells and animal cells. Learn about aerobic and anaerobic respiration.

Part of

KS3 Biology

This lesson includes:

  • three videos to help you understand about aerobic and anaerobic respiration
  • three practise activities to help reinforce learning


Energy is needed for life processes such as:

  • growth and repair
  • movement
  • control of body temperature in mammals

Respiration is a chemical reaction that happens in all living cells, including plant cells and animal cells. It is the way that energy is released from glucose so that all the other chemical processes needed for life can happen. Do not confuse respiration with breathing (which is properly called ventilation).

Aerobic respiration

  • Living things need energy to perform different tasks in order to survive
  • Aerobic respiration is a chemical reaction that transfers energy to cells
  • The waste products of aerobic respiration are carbon dioxide and water

In this film Jon Chase explains aerobic respiration:

Jon Chase explains aerobic respiration

Living things need energy for everything they do, including growing and reproducing.

This energy comes from glucose.

All animals and humans get glucose through eating it, but plants need to make their own glucose during photosynthesis.

Plants and animals transport glucose and oxygen to tiny structures in their cells, called mitochondria. Here, the glucose and oxygen take part in a chemical reaction.

The reaction is called aerobic respiration, and it produces energy which transfers to the cells.

Aerobic respiration makes two waste products: carbon dioxide and water.

Animals remove carbon dioxide from their bodies when they breathe out.

Plants use a different method. In daytime they use some of this carbon dioxide for photosynthesis. At night, they release the carbon dioxide to their surroundings.

A case study video on how an athlete uses aerobic respiration during exercise

Anaerobic respiration

During hard exercise, not enough oxygen can reach your muscle cells.

So, aerobic respiration is replaced with anaerobic respiration.

This does not need oxygen for it to happen.

  • Anaerobic respiration transfers energy from glucose to cells
  • It occurs when oxygen is not present
  • It transfers large amounts of energy quickly

Anaerobic respiration produces much less energy than aerobic respiration.

The waste product, lactic acid, builds up in the muscles causing pain and tiredness. This leads to cramp. Lactic acid is only broken down when you start aerobic respiration again.

Anaerobic respiration happens in microorganisms such as bacteria because they need to release energy from glucose too.

Yeast, which are unicellular fungi, can carry out an anaerobic process called fermentation.

A case study video on how an athlete uses anaerobic respiration during exercise

Aerobic and anaerobic respiration comparison

The table compares the main features of aerobic and anaerobic respiration:

Needs oxygen?YesNo
Needs glucose?YesYes
Product(s) formedCarbon dioxide and waterLactic acid


There are lots of fun ways to practise what you know about respiration.

Activity 1

Drag and drop the equation symbols for aerobic respiration:

Activity 2

Drag and drop the equation symbols for anaerobic respiration:

Activity 3

Try this respiration and gas exchange crossword from Twinkl:

Respiration and gas exchange crossword

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