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

How does enzyme concentration influence the rate of reaction?

1. Increased concentration leads to more successful collisions

2. Increased concentration leads to fewer successful collisions

3. Enzyme concentration has no effect on reaction rate

4. Decreased concentration speeds up the reaction rate

The correct answer is: Increased concentration leads to more successful collisions

Increasing the concentration of enzymes in a reaction generally leads to an increase in the rate of reaction. This is because a higher concentration of enzymes results in a greater availability of active sites for substrate molecules. With more enzymes present, the likelihood of substrate molecules colliding with those active sites increases, leading to more successful collisions. Successful collisions between enzyme and substrate facilitate the formation of enzyme-substrate complexes, which speeds up the conversion of substrates into products. As the reaction rate continues to increase with enzyme concentration, it is important to note that this trend can only continue up to a certain point, often when all substrate molecules are bound to enzymes or when the substrate is in limited supply. Beyond this point, adding more enzymes will not further enhance the reaction rate since there will be insufficient substrate for the excess enzymes to act on. This concept is pivotal in understanding enzyme kinetics and how enzymes function within biological systems.