Catabolism refers to metabolic pathways that:

• A. Metabolic pathways that construct molecules, requiring energy.
• B. Metabolic pathways that break down molecules, releasing energy.
• C. A measure of disorder or randomness.
• D. Measures the portion of a system's energy that can perform work.

Answer: (B)

Catabolic pathways break down complex molecules into simpler ones, releasing energy that the cell can capture as ATP and reduced cofactors like NADH and FADH2. This energy release powers cellular work and drives other processes. The other options describe different ideas: building molecules requires energy (anabolism); disorder is entropy; and energy available to do work is a thermodynamic measure (free energy), not a metabolic pathway type.