A Level Biology Practice Exam

Which process involves reactions that break molecules down into smaller units to release energy?

1. Anabolism

2. Catabolism

3. Photosynthesis

4. Cell Respiration

The correct answer is: Catabolism

The process that involves reactions breaking molecules down into smaller units to release energy is correctly identified as catabolism. Catabolic reactions encompass a range of metabolic pathways that break down complex molecules, such as carbohydrates, fats, and proteins, into simpler molecules. This breakdown process often involves hydrolysis reactions that release energy stored in chemical bonds. This released energy is then harnessed by the cell to perform various functions, including growth, repair, and maintenance. Catabolism is crucial in both providing substrates for anabolic processes and generating ATP, which is the primary energy currency in biological systems. In contrast, anabolism refers to the building-up processes that synthesize complex molecules from simpler ones, typically requiring an input of energy. Photosynthesis specifically involves the conversion of light energy into chemical energy stored in glucose, which does not primarily function to break down molecules for energy release. Cell respiration, while it does involve breaking down molecules for energy, can be considered a process that includes both catabolic and oxidative pathways, but the core activity of breaking down large molecules for energy specifically aligns with catabolism.