Year 11s test leaves for starch during investigations to establish photosynthesis.
Recent lab work in Biology has had Year 11s carry out starch tests on a leaf to prove that both light and chlorophyll (which allows plants to absorb energy from light) are needed for photosynthesis to take place.
The first stage of the experiment was to ‘kill’ the leaf by placing it in just-boiled water. Students then added enough ethanol to cover the leaf and remove the chlorophyll from it so, effectively, they had a clean slate with which to work.
The third step was to spread the leaf out on a white tile and cover it with iodine solution. If photosynthesis had indeed occurred, glucose would have been produced in the specimen and converted to starch. Since iodine solution changes from brown to black if starch is present, the area of the leaf that contained starch turned black while the area without remained brown.