Describe an experiment to prove that - Plant leaf has starch.
Answers
Answer:
Starch testing
Iodine solution is used to test leaves for the presence of starch. You need to:
heat a plant leaf in boiling water for 30 seconds (this kills the leaf, stopping any chemical reactions)
add the leaf to boiling ethanol in a water bath for a few minutes (the boiling ethanol dissolves the chlorophyll and removes the green colour from the leaf - it turns white so it is easy to see the change in colour)
wash with water to rehydrate and soften the leaf and spread onto a white tile
add iodine solution from a dropping pipette
After a few minutes, the parts of the leaf that contain starch turn the iodine from brown to blue/black.
Variegated leaves have green parts (where the cells contain chlorophyll) and white parts (where there is no chlorophyll). Only the parts that were green become blue/black with iodine solution, showing the importance of chlorophyll in photosynthesis. The parts without chlorophyll do not photosynthesise, and so they do not make starch and the iodine does not change colour.
Two variegated leaves. The left one has green parts which contain chlorophyll for photosynthesis. The right one has been treated with iodine. The parts containing chlorophyll turn blue-black.
The leaf on the left is a variegated leaf. The green parts contain chlorophyll and photosynthesise to make starch. The white part of the leaf does not contain chlorophyll, so does not photosynthesise.
The leaf on the right shows a positive test for starch in the areas which contained chlorophyll, and a negative test for starch in the areas which lack chlorophyll.
This is evidence that chlorophyll is required for photosynthesis.
A plant can be ‘de-starched’ by leaving it in the dark for a few hours. Parts of its leaves are covered with dark paper, and the plant is left in the light for a few hours. Only the uncovered parts become blue/black with iodine solution, showing the importance of light in photosynthesis.
Answer:
Experiment to test the presence of starch in leaves:
Take two healthy green potted plants of the same type. Keep on potted plant in a dark room for one or two days in order to remove all the starch from the leaves. Keep the other plant in sunlight. Now, take one leaf from each potted plant and put a few drops of iodine solution on them. Then note down the observation.
Plants kept in light and dark conditions
No blue black color will be observed on the leaves of the plant kept in the dark room. This indicates the absence of starch. Blue black color will be observed on the leaves of the plant kept in sunlight. This indicates the presence of starch.
These are the ways to test the presence of starch
Explanation: