Activation energy is the minimum amount of energy required for a chemical reaction to occur. It acts as a barrier that reactants must overcome to transform into products. This energy can come from various sources, such as heat or light, and is essential for initiating reactions in both biological and chemical processes. In many cases, catalysts are used to lower the activation energy, making it easier for reactions to take place. For example, in living organisms, enzymes are biological catalysts that speed up reactions by reducing the activation energy needed, allowing processes like metabolism to occur efficiently at body temperature.