OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

Why are enzymes essential for biological reactions?

1. They slow down reactions.

2. They increase the temperature of the reactions.

3. They act as catalysts to speed up reactions.

4. They consume substrates in reactions.

The correct answer is: They act as catalysts to speed up reactions.

Enzymes are essential for biological reactions because they act as catalysts that significantly speed up the rate of these reactions without being consumed in the process. This is crucial for the functioning of biological systems, as many biochemical reactions would occur too slowly at the temperatures and conditions present in living organisms to support life. By lowering the activation energy required for a reaction to occur, enzymes enable biochemical processes to proceed at a rate that sustains cellular functions and overall metabolism. For instance, in cellular respiration, enzymes facilitate the breakdown of glucose to release energy much more rapidly than would occur without them. This catalytic function allows the necessary chemical reactions to occur under milder conditions, preserving the integrity of organic molecules and enabling complex metabolic pathways to operate efficiently. The other options highlight incorrect concepts about enzymes. Unlike the first option, enzymes do not slow down reactions; instead, they enhance their speed. The second option, which suggests that enzymes increase temperature, is also incorrect, as enzymes work effectively at specific temperature ranges without directly causing temperature changes. Lastly, the idea that enzymes consume substrates misrepresents their role; instead, enzymes interact with substrates to form products without changing or using up themselves.