Lesson 5 of 5

Aerobic or anaerobic?

Goal: Compare aerobic and anaerobic respiration.

Puzzles for this lesson

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A cyclist riding at a steady pace along a flat path
A long, steady ride. The blood brings all the oxygen the muscles need, so respiration is aerobic.
Children sprinting in a race on a school field
A sprint. Oxygen cannot arrive fast enough, so the muscles respire anaerobically as well.

Both kinds of respiration release energy from glucose. Only aerobic respiration needs oxygen.

Aerobic respirationAnaerobic respiration

The energy released from one glucose molecule. Aerobic respiration releases many times more.

Aerobicglucose + oxygen → carbon dioxide + water
AnaerobicIn muscles: glucose → lactic acid
In yeast: glucose → ethanol + carbon dioxide
  • The same: both happen in living cells, both use glucose and both release energy.
  • Different: only aerobic respiration needs oxygen, and it releases far more energy. The products are different too.
  • Most living things respire aerobically most of the time. They switch to anaerobic respiration when oxygen runs short.

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Key words in this lesson

Respiration A chemical reaction in cells that releases energy from glucose

Aerobic respiration Respiration that uses oxygen

Anaerobic respiration Respiration without oxygen

Glucose The sugar that cells break down in respiration

Oxygen The gas that aerobic respiration uses up

Carbon dioxide The gas made in aerobic respiration and in fermentation

Lactic acid The product of anaerobic respiration in muscles

Yeast A fungus made of single cells, used to make bread and beer

Ethanol The alcohol made in fermentation

Product A substance that is made in a chemical reaction

For teachers: AQA 3.9.3 · Pearson Edexcel 1.5