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Experiments Conducted to Prove the Formation of Starch in Plants

Given below i...

Question

Given below is a sketch of a leaf partially covered with black paper and which is to be used in the experiment to show that light is compulsory for the process of photosynthesis:

(a) At the end of the experiment, which of the leaf part/leaf parts labelled I, II and III will become blue-black when dipped in iodine solution?
(b) Which substance will be missing in the leaf part/leaf parts which will not become blue-black when dipped in iodine solution?

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Solution

(a) Parts I and III will appear blue black in colour which indicates the presence of starch in these regions.
(b) Part II will not appear blue black in colour because starch will be missing from that part. The black paper in region II will prevent the sunlight from reaching that region, as a result of which no starch synthesis would occur.

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Q. A star-shaped figure was cut in the black paper strip used for covering the leaf of a destarched plant used for demonstrating that light is necessary for photosynthesis. At the end of the experiment when the leaf was tested for starch with iodine, the star-shaped figure on the leaf was found to be:

(1) colourless
(2) green in colour
(3) brown in colour
(4) blue-black in colour

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.
(a) Which substance could not be synthesised in the green leaf?
(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 the experiment to show that sunlight is necessary for photosynthesis:
(a) What is done to destarch the green leaves of the potted plant initially?
(b) What is done to a part of destarched leaf so that photosynthesis may not take place in that part of the leaf (before keeping the potted plant in sunlight)?
(c) How is chlorophyll removed from the green leaf before further testing?
(d) Which reagent is used to test the presence/absence of starch in the parts of experimental leaf?

Q. Both the plants 'A' and 'B' were kept in sunlight after watering. The part of the leaf of plant 'B' which was inserted in the glass bottle containing KOH(Potassium hydroxide) did not turn blue in the iodine test/ starch test, indicating the absence of starch. The part of the leaf outside the bottle turns blue in the said test. Photosynthesis didn't occur in that part of the leaf due to the non-availability of _________.

Q. Before testing the leaf for starch at the end of the experiment "Light is necessary for photosynthesis":
(a) In which liquid the leaf should be boiled?
(b) Why should the leaf should be boiled in this liquid?

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Experiments Conducted to Prove the Formation of Starch in Plants

Standard XII Biology

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