Decay is the process by which dead animal or dead plant matter is broken down to simple compounds. These simpler products can then be used as food by living things, such as plants. Decay is an important process in the environment (see Food chain). Decay removes the wastes that animals give off and the plants and animals that die. Decay is sometimes called decomposition or putrefaction. 
The major part of the decay process is carried out by microbes, such as bacteria, molds, and yeasts. Such microbes feed on and completely digest dead animal or plant matter, or the waste products of live animals. During decay, enzymes in the microbes break down macromolecules (large molecules). For example, the enzymes convert proteins to amino acids and complex carbohydrates to simple sugars. The microbes use these products to build the materials they need. They also use some of the products to get energy for growth and reproduction. As the microbes grow and multiply, the decay process speeds up. See Decomposer.
Warmth and moisture help microbes grow and thus assist the decay process. Refrigeration or cooking kills microbes and slows decay. Certain chemicals also can destroy microbes and prevent decay.
The decay of animals and plants is important in geology. For example, coal and petroleum are formed from plants that became buried in swamps and decayed. See Fossil fuel.
