A green leaf that has fallen down from a plant is taken and is kept in hot water for sometime and then taken out. It is then dipped in spirit and iodine solution. The leaf turns bluish indicating the presence of ___.

protein

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starch

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fats

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carbohydrates

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Solution

The correct option is B starch
Starch test is done using iodine solution. Plants prepare food, by a process called photosynthesis, which is stored as starch. When the fallen leaf is kept in hot water for sometime and then dipped in iodine solution, it turns bluish indicating that the leaf was performing photosynthesis and contains starch.

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Q. Arun carried out the following experiment with a croton (variegated) leaf. He drew the leaf in his notebook marking the green and the non-green area. He put the leaf in hot alcohol till all the green colour came out and the leaf turned white. He then washed the leaf in water and covered the leaf in iodine solution.
(a) Why did he draw the leaf and mark the green and non-green areas?
(b) What was the colour change in iodine solution?
(c) Which portions of the leaf show colour change?
(d) what can you conclude from this experiment?

Q. Complete the following paragraph by filling in the blanks (i) to (v) with appropriate words:
To test a leaf for starch, the leaf is boiled in water to (i) .......... . It is then boiled in Methylated spirit to (ii) .......... . The leaf is dipped in warm water to soften it. It is placed in a petri dish, and (iii) ........... solution is added. The region of the leaf which contains starch turns (iv) .......... and the region which does not contain starch, turns (v) ........... .

Q. Question 1. What happens to the colour of the leaf? What is the colour of the solution?

Now dip the leaf in a dilute solution of iodine for a few minutes.
Take out the leaf and rinse off the iodine solution.
Observe the colour of the leaf and compare this with the tracing of the leaf done in the beginning.

Question 2. What can you conclude about the presence of starch in various areas of the leaf?

Why is the leaf boiled in water and alcohol before testing for the presence of starch?

Two potted green plants of the same kind were taken to perform an experiment. One of them was kept in a dark room, while the other one was kept in sunlight for 3–4 days. A leaf from each of the plant was taken to perform the iodine test. Which of the leaves turned blue-black in colour and why? [5 MARKS]

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