Biological catalysts, known as enzymes, are proteins that speed up chemical reactions in living organisms. They lower the activation energy needed for reactions, allowing processes like digestion and metabolism to occur more efficiently. Each enzyme is specific to a particular reaction or type of substrate, which is the molecule it acts upon. Enzymes function by binding to their substrates at a specific site, forming an enzyme-substrate complex. This interaction facilitates the conversion of substrates into products. Factors such as temperature, pH, and concentration can affect enzyme activity, making them essential for maintaining proper biological functions in cells.