A substrate is a surface or material on which an organism lives, grows, or is attached. In biology, it often refers to the base layer that supports the growth of plants, fungi, or microorganisms. For example, in a garden, soil acts as a substrate for plants, providing nutrients and stability. In chemistry, a substrate is a substance that undergoes a reaction in the presence of a catalyst, such as an enzyme. The enzyme binds to the substrate, facilitating a chemical reaction. This concept is crucial in understanding processes like metabolism in living organisms, where substrates are transformed into products.