What is the difference between aerobic and anaerobic respiration?

Aerobic respiration needs oxygen. It is the release of a relatively large amount of energy in cells by the breakdown of food substances in the presence of oxygen:

glucose + oxygen → carbon dioxide + water

Aerobic respiration happens all the time in animals and plants. Most of the reactions in aerobic respiration happen inside mitochondria in cells.

Anaerobic respiration happens in muscles during hard exercise:

glucose → lactic acid

C₆H₁₂O₆ → 2C₃H₆O₃

Glucose is not completely broken down, so much less energy is released than during aerobic respiration.

There is a build-up of lactic acid in the muscles during vigorous exercise. The lactic acid needs to be oxidised to carbon dioxide and water later.