Which of the following correctly describes catabolism?

Catabolism is correctly described as the breaking down of complex molecules. This process involves the degradation of larger, more complex macromolecules into smaller, simpler units. It serves several important functions in the body, such as providing energy, which is crucial for various physiological processes, and recycling cellular components. During catabolic reactions, energy stored in the chemical bonds of complex molecules is released, often in the form of adenosine triphosphate (ATP), which cells can then use to perform work.

The other choices do not accurately define catabolism. The building up of complex molecules refers to an anabolic process, which is the opposite of catabolism. Synthesis of proteins is a specific type of anabolic reaction, not a description of catabolic processes. Likewise, the formation of new cells also pertains more to growth, repair, and development of tissues, which involve anabolic pathways rather than catabolic ones.