A class investigates the digestion of starch by saliva. Samples of the reaction mixture are tested with iodine solution 1, 3 and 5 minutes after the saliva and starch are mixed.
| Time after mixing in minutes | Colour of the iodine solution |
|---|---|
| 1 | Blue-black |
| 3 | Blue-black |
| 5 | Orange-brown |
Which conclusion is supported by these results?
Sugar was present at 1 minute but not at 5 minutes
Some starch was still present in the mixture at 3 minutes
All of the starch had been digested by 3 minutes
Starch was present at 5 minutes but not at 1 minute
304 exam-style questions on AQA GCSE Biology 2.2 Animal tissues, organs and organ systems, covering 2.2.1 The human digestive system, 2.2.2 The heart and blood vessels, 2.2.3 Blood, 2.2.4 Coronary heart disease: a non-communicable disease, 2.2.5 Health issues, 2.2.6 The effect of lifestyle on some non-communicable diseases, and 2.2.7 Cancer. Each one has a worked solution and a mark scheme showing where the marks go.