Anaerobic respiration

Living things can respire without oxygen too. Respiration without oxygen is anaerobic respiration.

In plant cells and yeast — alcoholic fermentation

glucose → carbon dioxide + ethyl alcohol + energy

Yeast growing in a sugar solution is an example.

In animal cells — lactic acid fermentation

glucose → lactic acid + energy

It happens in human muscles too.

After a 100 m sprint

After fast exercise such as a 100 m race, the leg muscles ache and cramp. Anaerobic respiration in the muscles has built up lactic acid.

Aerobic respiration gives much more energy: it breaks glucose down completely, while anaerobic respiration breaks it down only partly.