Catabolism refers to the exergonic process by which energy released by the breakdown of organic compounds such as glucose can be used to synthesize ATP, the form of energy required to do cellular work. Anabolism is the endergonic process that uses the energy stored in ATP to synthesize the building blocks of the macromolecules that make up the cell. Precursor metabolites are intermediate molecules in catabolic and anabolic pathways.
Thumbnail: Plant cells (bounded by purple walls) filled with chloroplasts (green), which are the site of photosynthesis. (CC BY-SA 3.0; Kristian Peters).