We have an activity to show that 'Chlorophyll is essential for photosynthesis'
1. We take a potted plant like croton whose leaves are partly green and partly white. The green part of the leaf has chlorophyll but the white part of the leaf does not have chlorophyll.
2. Place this plant in a completely dark place for about three days to destarch its leaves.
3. Take out the potted plant from the dark place and keep it in bright sunshine for three to four days.
4. Pluck the variegated leaf from the plant, boil it in water for a few minutes and then remove its green colour 'chlorophyll' by boiling it in alcohol. The green parts of the leaf get decolourised. So, we get decolourised leaf.
5. Wash the decolourised leaf with hot water to soften it and remove any chlorophyll which may be sticking to it.
6. Pour iodine solution over the colourless leaf and observe the change in colour of the leaf.
7. We will find that the outer part of leaf that was originally white (without chlorophyll) does not turn blue-black on adding iodine solution showing that no starch is present in this outer part of the leaf. From this observation we conclude that the photosynthesis to make starch does not take place without chlorophyll.
8. The inner part of leaf which was originally green (contained chlorophyll) turns blue-black on adding iodine solution showing that starch is present in this inner part of the leaf. From this observation we conclude that the photosynthesis to make starch takes place in the presence of chlorophyll. In other words, chlorophyll is necessary for the process of photosynthesis to take place.
The questions are-
1) Glucose is formed during photosynthesis but then why in the above experiment, test for starch was performed?
2) Why is it important to place the plant in dark before the experiment?
3) WHy do we boil the leaf in alcohol?
4) Why do we need to decoulorise the leaf?
5) A water bath is used for boiling of leaf in alcohol. Why?
6) What are the features in a a green leaf that makes it suitable for photosynthesis?
Answers
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Answer no.6- ..... Chlorophyll present in a green leaf that makes it suitable for photosynthesis....
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1 . because glucose stored as a starch as leaf.
2 . to destarch it leaf
3 . to remove the cholorophyll
4 .to observe the color simply
5 .because alcohal is more flameable
6 . it contain chlorophyll
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