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, soil serves 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. Enzymes, which are biological catalysts, interact with substrates to facilitate chemical reactions. For instance, in the process of digestion, enzymes break down food substrates into simpler molecules for absorption.