What is the difference between anabolism and catabolism?

The distinction between anabolism and catabolism lies in their respective roles in metabolic processes. Anabolism refers to the series of chemical reactions that construct complex molecules from simpler ones, a process that often requires an input of energy. This energy is typically derived from the breakdown of ATP (adenosine triphosphate), which fuels the formation of these larger biomolecules essential for cellular structure and function, such as proteins, nucleic acids, carbohydrates, and lipids.

In this context, the correct choice emphasizes that anabolism not only builds complex structures but also consumes energy in the process. This is essential for maintaining and growing cellular components.

Conversely, catabolism is the set of metabolic pathways that breaks down complex molecules into simpler ones, releasing energy that can then be stored or used for intermediate metabolite synthesis or for driving anabolic reactions. Thus, understanding that anabolism requires energy input while dealing with the synthesis of macromolecules highlights why the selected answer accurately reflects the relationship between these two metabolic processes.