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Photosynthesis

Arun carried ...

Question

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?

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Solution

(a) Arun drew the leaf and marked the green and the non-green areas to identify the part of the leaf that can make food in the form of starch.
(b) The colour of the iodine solution turned blue-black from brown.
(c) The green portions of the leaf show the change in colour.
(d) We can conclude that the green portion of the leaf can make food, i.e. starch, in the presence of sunlight. This is because this portion has chlorophyll.

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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?

Q. 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 ___.

Q. In an experiment, a destarched, long and narrow green leaf (still attached to a potted plant) is introduced into a wide-mouthed glass bottle through an airtight cork. The glass bottle contains some potassium hydroxide solution in its lower part (but the leaf remains above this solution). The whole set-up is placed in sunlight for 2-3 days. The leaf is then taken out. After removing chlorophyll, the leaf is treated with iodine solution. No blue-black colour is produced in the leaf.
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(b) What is the function of potassium hydroxide solution inside the glass bottle?
(c) Which condition necessary for photosynthesis is not fulfilled in this experiment?

Q. In an experiment to test the presence of starch in a leaf, the plucked leaf is first boiled in water for a few minutes. This is an important step in the experiment because it :
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A healthy croton plant bearing variegated leaves was kept in a dark cupboard to destarch it, after which it was placed in sunlight for a few hours. One of the leaves was then plucked and any outline of the leaf making the green and non-green regions were drawn. The leaf was then tested for starch. Using the above information, answer the following question

What change is seen on the leaf after the starch test ?

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