Aim:
To test various leaves for the presence of starch
Hypothesis:
After the iodine reagent is added, the green areas on the leaf, where starch is supposedly present, will turn to a blue-black colour – the positive test for starch.
Method:
- Obtain your leaf and cut a small sample of your leaf;
- Immerse the leaf samples in hot water for 1-2 minutes (depending on the size of the leaf samples)
- Remove the leaf samples from the hot water and keep them carefully to one side.
- Half fill a boiling tube with alcohol and place the tube in hot water until bubbles start to form in the alcohol.
- Place the leaf samples in the hot alcohol for about 5 minutes.
- When the samples have decolourised, remove them from the hot alcohol using a glass rod.
- Place the leaf samples back into the hot water for a few seconds; be careful as they could be fragile.
- Remove the samples from the hot water and spread them out onto a white tile
- Drop iodine reagent onto the leaf samples, you may need to wait for a few minutes
- Repeat experiment
- Write observations
- Draw conclusions
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Teacher Reviews
Here's what a teacher thought of this essay
This report on the starch test on leaves adequately describes the method and likely outcome of the test for green leaves grown in the light. GCSE exam questions very rarely ask for this method but focus on investigations where the plant has been denied one factor required for photosynthesis. The writer does mention that a positive result was achieved only for the green areas of the leaf and the essay would have benefited from a discussion of variegation in plants where leaves have both green and white areas. The writer's method is a little vague in places and would be difficult to repeat since exact details of size and temperature are omitted. 3 stars
