An enzyme from plant cells joins glucose molecules to make starch. A student measures the rate of this reaction at different enzyme concentrations. The temperature and pH are kept at their optimum values, and the same amount of glucose is used each time.
| Enzyme concentration in g dm⁻³ | Rate of reaction in arbitrary units |
|---|---|
| 0.2 | 6 |
| 0.4 | 12 |
| 0.6 | 17 |
| 0.8 | 18 |
| 1.0 | 18 |
Which interpretation best explains why the rate stops increasing at the highest enzyme concentrations?
The enzyme molecules are used up as starch is made
The extra enzyme has changed the shape of the active sites
The amount of glucose has become the limiting factor
All the active sites are occupied by glucose
184 exam-style questions on OCR GCSE Biology 1.2 What happens in cells (and what do cells need)?, covering 1.2.1 Structure of DNA, 1.2.2 Nucleotides and complementary bases, 1.2.3 Protein synthesis, 1.2.4 DNA structure and the proteins made, 1.2.5 Investigating enzymatic reactions, and 1.2.6 Mechanism of enzyme action. Each one has a worked solution and a mark scheme showing where the marks go.