Enzymes are biological catalysts that speed up chemical reactions in living organisms. There are more than five hundred different enzymes in every cell of the body, each of them helping the cell, and the body as a whole, to work.
Some enzymes work outside the cells, for example the enzymes in the digestive system.
Enzymes are involved in all biological reactions, e.g. cellular respiration, photosynthesis and protein synthesis. Without enzymes these vital reactions would be too slow for life to continue.