Which of the following describes the breakdown of complex substances into simpler ones with the release of energy?

The breakdown of complex substances into simpler ones with the release of energy is referred to as catabolism. This process is a crucial part of metabolism, which is the sum of all biochemical reactions in the body, including both catabolic and anabolic reactions. During catabolism, larger molecules such as carbohydrates, fats, and proteins are broken down into smaller units like glucose or amino acids, which can then be used by the body for energy. This energy release is significant for various bodily functions, including cellular respiration and physical activity.

In contrast, anabolism describes the synthesis of complex molecules from simpler ones, which typically requires energy input. Synthesis is closely related to anabolism as it involves the construction of substances rather than their breakdown, while metabolism encompasses both catabolic and anabolic pathways. Thus, the distinct function of catabolism in energy release makes it the correct choice for describing this specific process.