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The steps below are involved in the testing of a leaf for starch. Study them car...


Question

The steps below are involved in the testing of a leaf for starch. Study them carefully and answer the question

I. Place the leaf in the boiling water and boil for 2 minutes.

II. Place the boiled leaf in a boiling tube containing 90% ethanol. Gently remove the leaf and wash with a fine trickle of cold tap water.

III. Remove a green leaf from a plant that has been exposed to sunlight for a few hours.

IV. Add a few drops of iodine/potassium iodide solution to the leaf and note any observations.

The CORRECT order for the test is

Options

A) I, II, III and IV

B) I, III, II and IV

C) II, III,, I and IV

D) III, I, II and IV


The correct answer is D.

Explanation:

The steps below are involved in the testing of a leaf for starch.
1. Remove a green leaf from a plant that has been exposed to sunlight for a few hours
2. Half-fill a 250cm3 beaker with water. Heat the water until it boils. Keep the water at boiling point.
3. Use the forceps to place the leaf in the boiling water. Boil for 2 minutes.
4. Turn off the Bunsen Burner. (If you are using a heat source without a naked flame - electric water bath or hot plate - this step is unnecessary.)
5. Place the boiled leaf in a boiling tube containing 90% ethanol.
6. Place the boiling tube in hot water and boil for 10 minutes or until the leaf decolourizes. ( It may be necessary to replace the ethanol)
7. Gently remove the leaf and wash with a fine trickle of cold tap water.
8. Spread the leaf evenly on a white tile.
9. Add a few drops of iodine/potassium iodide solution to the leaf and note any observations.


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Dicussion (1)

  • The steps below are involved in the testing of a leaf for starch.
    1. Remove a green leaf from a plant that has been exposed to sunlight for a few hours
    2. Half-fill a 250cm3 beaker with water. Heat the water until it boils. Keep the water at boiling point.
    3. Use the forceps to place the leaf in the boiling water. Boil for 2 minutes.
    4. Turn off the Bunsen Burner. (If you are using a heat source without a naked flame - electric water bath or hot plate - this step is unnecessary.)
    5. Place the boiled leaf in a boiling tube containing 90% ethanol.
    6. Place the boiling tube in hot water and boil for 10 minutes or until the leaf decolourizes. ( It may be necessary to replace the ethanol)
    7. Gently remove the leaf and wash with a fine trickle of cold tap water.
    8. Spread the leaf evenly on a white tile.
    9. Add a few drops of iodine/potassium iodide solution to the leaf and note any observations.

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