Question

Write an experiment to show that chlorophyll is necessary for photosynthesis.

Answer 1

Hint: Chlorophyll is any of several related green pigments found in the mesosomes of cyanobacteria and in the chloroplasts of algae and plants. Chlorophyll is concentrated within organisms in structures called chloroplasts grouped inside plant cells. Two types of chlorophyll exist in the photosystems of green plants: chlorophyll \[a\] and \[b\].

Complete answer:
1.Take a potted plant with variegated leaves and keep it in a dark region, away from sunlight for about \[3\] days. This will halt photosynthesis and destarch the plant.
2.Then keep the plant facing the sunlight for \[6 - 8\] hours. The plant can again carry out photosynthesis and produce starch.
3.Mark the green areas in the leaf and trace them on a sheet of paper. Mark the regions as green and yellow. The green areas contain chlorophyll which is absent in the yellow areas.
4.Immerse the leaf in boiling alcohol to decolourize it. Leaf slowly loses its green colour, which goes into the alcohol.
4.Dip this decolorized leaf in iodine solution. Now remove the leaf from iodine solution and rinse it in distilled water. Remove the leaf from distilled water and keep it on a petri dish.
6.Two colour regions are visible in the leaf. They are reddish brown and blue-black.
It can be concluded that the earlier green parts of the leaf turn blue-black whereas the yellow parts have become reddish brown.
Green parts of the leaf possess chlorophyll and hence they carry out photosynthesis and produce starch, which turns blue-black with iodine.

Note:
Variegated leaves can be found in plants like Coleus, Tradescantia and Croton. A variegated leaf includes different patches of colours like green, yellow, white, brown etc. A green patch in the leaf includes chlorophyll while other coloured patches in the leaf include other coloured pigments other than chlorophyll. The above experiment is also called iodine test. The green patches of leaves give a positive test for starch.