(iii) Describe how to safely test the leaves for starch. (b) Explain how the results of this experiment would show that a plant needs light for photosynthesis.

4. (a) (iii) To safely test the leaves for starch: 1. Boil the leaf in water for a few minutes. This kills the cells and breaks down the cell walls and membranes, making it easier for iodine to penetrate. 2. Decolorize the leaf: Place the boiled leaf in a test tube containing ethanol (alcohol). Place this test tube in a beaker of hot water (a water bath). Do not heat ethanol directly over a flame as it is flammable. The ethanol will remove the chlorophyll, making any colour change from the iodine test visible. 3. Rinse the leaf: Remove the leaf from the ethanol and rinse it thoroughly with cold water to rehydrate it and remove any remaining ethanol. 4. Test for starch: Spread the leaf on a white tile and add a few drops of iodine solution. Observe any colour change. 4. (b) The results of this experiment would show that a plant needs light for photosynthesis by comparing the starch test results of leaf Y: The part of leaf Y that was exposed to light would turn blue-black when tested with iodine solution, indicating the presence of starch. The part of leaf Y that was covered by black paper (and therefore deprived of light) would remain brownish-yellow (the colour of iodine solution), indicating the absence of starch. This difference in starch presence demonstrates that light is essential for the plant to carry out photosynthesis and produce starch. What's next?