What are catalysts?

A catalyst is something that speeds up the rate of a reaction. In biology, enzymes are catalysts. Enzymes are proteins that allow reactions to carry out. For example, in order to break down the storage molecules glycogen into its subunits of glucose, you need an enzyme to break the bonds and release the glucose. Without enzymes, most reactions in the body would occur too slowly in order for humans to function

A catalyst is a substance that speeds up a chemical reaction without being used up itself.

A catalyst is something that increases the rate of a reaction by lowering the activation energy but is not used in a reaction and does not affect the products. Enzymes are biological catalysts.