A student tests samples from an amylase–starch mixture with iodine every 10 s.
Table
| Time / s | Colour with iodine |
|---|---|
| 20 | blue-black |
| 30 | blue-black |
| 40 | orange-brown |
| 50 | orange-brown |
Which statement about the time when starch disappeared is supported by these results?
It was after 20 s20\,\mathrm{s}20s and at or before 30 s30\,\mathrm{s}30s.
It was after 30 s30\,\mathrm{s}30s and at or before 40 s40\,\mathrm{s}40s.
It was after 40 s40\,\mathrm{s}40s and at or before 50 s50\,\mathrm{s}50s.
It was after 10 s10\,\mathrm{s}10s and at or before 20 s20\,\mathrm{s}20s.
44 exam-style questions on Edexcel GCSE Biology 1.3 Enzymes, covering 1.3.1 Mechanism of enzyme action, 1.3.2 Denaturation of enzymes, 1.3.3 Factors affecting enzyme activity, and 1.3.4 Measuring energy in food by calorimetry. Each one has a worked solution and a mark scheme showing where the marks go.