GCSE Biology Practice Exam 2026 – Comprehensive Study Resource

When an enzyme's active site does not match the substrate, the specific shape and configuration of the active site prevent the substrate from binding effectively. Enzymes are highly specific biological catalysts, and their functionality is largely dependent on the precise fit between the enzyme and its substrate, often referred to as the "lock and key" model or the "induced fit" model.

If there is no proper fit, the enzyme-substrate complex cannot form, which means that the enzyme cannot facilitate or catalyze the chemical reaction associated with that particular substrate. Therefore, the reaction will not occur. This principle is fundamental to understanding enzyme specificity and activity in biological processes.

Other options imply alternative scenarios such as catalysis occurring, substrate decomposition, or enzyme denaturation, which are not accurate when considering the mismatch between an enzyme’s active site and its substrate.