Enzymes are biological catalysts that speed up chemical reactions in living organisms. They work by lowering the activation energy needed for a reaction to occur, allowing processes like digestion and metabolism to happen more efficiently. Each enzyme is specific to a particular substrate, meaning it only works on certain molecules. Enzymes are crucial for various functions in the body, such as breaking down food into nutrients and facilitating cellular processes. For example, the enzyme amylase helps break down carbohydrates, while lipase aids in fat digestion. Without enzymes, many essential reactions would occur too slowly to sustain life.