A level west mock biology paper 2

1. (a) State the role of enzymes in metabolic pathways.
Enzymes act as biological catalysts that speed up biochemical reactions by lowering the activation energy without being consumed in the process. They ensure reactions occur at a suitable rate under physiological conditions.

1. (b) Explain why metabolic reactions occur in gentle steps.
Metabolic reactions occur in gentle, controlled steps to allow for efficient energy capture (e.g., ATP synthesis), prevent the release of damaging amounts of heat, and enable precise regulation at multiple points within the pathway.

1. (c) Describe the stages of the light independent reactions in a typical C3 plant.
The light-independent reactions (Calvin cycle) occur in three main stages:

• Carbon fixation: Carbon dioxide ($\text{CO}_2$) combines with a five-carbon sugar, ribulose-1,5-bisphosphate (RuBP), catalyzed by the enzyme RuBisCO. This forms an unstable six-carbon intermediate that immediately splits into two molecules of 3