Section A (multiple-choice questions with one correct answer)

Enzymes and metabolism are central themes in IB Biology, explaining how living organisms carry out the countless chemical reactions needed for life. Metabolism encompasses all enzyme-catalysed reactions within a cell, including pathways that build molecules and pathways that break them down. Enzymes provide the precise control and efficiency these reactions require, lowering activation energy and ensuring that metabolic processes occur rapidly and in tightly regulated sequences. Understanding enzyme structure, specificity, and the factors that influence enzyme activity is essential for explaining how cells maintain homeostasis and respond to changing conditions.