starch in leaf lesson

• Photosynthesis is the process by which plants use

• sunlight, water,

• and carbon dioxide

• to create oxygen and energy in the form of sugar

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1. heat a plant leaf in boiling water for 30 seconds (this kills the leaf, stopping any chemical reactions)

2. add the leaf to boiling ethanol in a water bath for a few minutes (the boiling ethanol dissolves the chlorophyll and removes the green colour from the leaf - it turns white so it is easy to see the change in colour)

3. wash with water to rehydrate and soften the leaf and spread onto a white tile

4. add iodine solution from a dropping pipette

After a few minutes, the parts of the leaf that contain starch turn the iodine from brown to blue/black.

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Variegated leaves have green parts (where the cells contain chlorophyll) and white parts (where there is no chlorophyll). Only the parts that were green become blue/black with iodine solution, showing the importance of chlorophyll in photosynthesis. The parts without chlorophyll do not photosynthesise, and so they do not make starch and the iodine does not change colour.

note: see you in the quiz​, study hard