Question

3. How will you test the presence of starch?​

Answer 1

Presence of starch in leaves can be tested by iodine test. Iodine turns starch solution into blue-black colour. Pour few drops of dilute iodine solution on the boiled leaf. The leaf becomes blue-black which proves the presence of starch in it.

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Answer 2

Answer:

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Starch is a white, powdery substance consisting of glucose which is used by plants as food. The presence of starch in leaves is evidenced enough of the process of photosynthesis being carried out in leaves as the formation of starch necessitates photosynthesis.

Requirements:

• Sample plants

• Glass jar or beaker

• Stove and saucepan

• Iodine solution

• Ethyl alcohol

• Tweezer

Procedure:

• Set up one plant on a sunny windowsill and another in a dark room for 24 hours

• After 24 hours, fill a beaker with ethyl alcohol and place it in a saucepan full of water

• Continue heating the pan until ethyl alcohol starts boiling and then take it off from the heat

• With the help of tweezers, dip each of the leaves in hot water for a minute

• Now, dip the leaves in the beaker holding ethyl alcohol for 120 seconds or till they change their color to almost white

• Place each of them in a shallow dish

• Cover these leaves with some drops of iodine solution and observe

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