Activity to demonstrate that chlorophyll is essential for photosynthesis
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Answer :
To demonstrate that chlorophyll is essential for photosynthesis.
Requirements : A potted plant with variegated leaves - for example, Croton or money plant (variegated leaves are partly green and partly white), rice paper, pencil, white paper sheath, beaker, test tube, 70% alcohol, KL solution, water bath.
Method : Keep the potted plant with variegated leaves in dark for three days so that the leaves become free from starch. Then place the plant in bright sun light for about 6 hours. Take a variegated leaf of the potted plant kept in bright sunlight. Trace the outline of leaves and its variegated parts on the tracing paper (the variegated leaves show pale yellow spots in green leaves. These areas indicate the absence of chlorophyll). Dip the leaf in boiling water for a few minute. Now boil the leaf in 70% alcohol till it decolorizes. Now dip the leaf in boiled water to make the leaf soft. Take out the leaf and stain with iodine (KL) solution. Observe the change in colour.
Observation : The blue colour appears only in those parts of leaf which were green in colour. The blue colour will not appear in variegated parts. This shows that starch formation takes place only in green (chlorophyll containing) parts of the leaf. Thus, the chlorophyll is essential for photosynthesis.