Respiration

Aerobic and anaerobic respiration

Respiration releases energy from glucose in every living cell. Aerobic respiration uses oxygen, happens in mitochondria and releases lots of energy: $\mathrm{C_6H_{12}O_6+6O_2\rightarrow6CO_2+6H_2O}$. Anaerobic respiration happens without oxygen and releases much less energy. In muscles: glucose → lactic acid; this builds up during vigorous exercise, causing fatigue and an oxygen debt repaid afterwards by fast breathing. In yeast: glucose → ethanol + carbon dioxide (used in brewing and baking). Energy is used for muscle contraction, protein synthesis, cell division, active transport, growth, nerve impulses and keeping warm.