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How will you test a leaf for starch, also mention precautions to be taken.
Starch Testing Experiment
Requirements:
1. Two plants
2. Beaker or glass jar
3. Saucepan on the stove
4. Ethyl alcohol
5. Iodine solution
6. Tweezers
Test for starch in plants:
1. Keep one of the plants in a dark room and another one on a sunny windowsill for 24 hours.
2. Fill the beaker or jar with ethyl alcohol. Keep it in a saucepan full of water. Heat the pan until the ethyl alcohol begins to boil.
3. Dip each of the leaves in the hot water for 60 seconds and then in the ethyl alcohol for 2 minutes or until they turn almost white. Keep them aside in a separate shallow dish.
4. Cover the leaves with iodine solution and observe.
Reaction: The hot water kills the leaf and the alcohol breaks down the chlorophyll. This removes the green colour of the leaf. When we put iodine on the leaves one of them will turn blue-black and the other will be a reddish-brown. Because the leaf that was in the light performed photosynthesis and produced starch. Iodine is an indicator that turns blue-black in the presence of starch.
Precaution: Keep ethanol away from naked flames. Wear eye protection while working with ethanol and iodine solution.
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