Within metabolism, which process typically requires energy input?

Anabolism is the process that typically requires energy input because it involves the synthesis of complex molecules from simpler ones. This is essential for growth, repair, and the maintenance of cells, as it allows for the construction of macromolecules such as proteins, nucleic acids, carbohydrates, and lipids.

During anabolic reactions, energy is often derived from adenosine triphosphate (ATP) or other high-energy molecules. For instance, when amino acids are linked together to form proteins, or when glucose molecules are combined to form glycogen, energy must be supplied to drive these reactions forward, against the thermodynamic tendency toward disorder.

In contrast, catabolism breaks down complex molecules into simpler ones, releasing energy in the process. Cellular respiration and fermentation are also processes that either release or harness energy from organic compounds, but do not typically require energy input in the manner that anabolic processes do. Therefore, the focus on building and synthesizing new structures makes anabolism distinctly energy-dependent.