how would you show that chlorophyll is necessary for photosynthesis?
Answers
Answer:
Aim of the experiment:-
To prove that chlorophyll pigment in green leaves is necessary for the plants to prepare their carbohydrate (starch) food.
Requirements for the experiment:-
A well watered variegated leaf plant, beaker, water, Bunsen burner, mentholated spirit or rectified spirit or ethanol, iodine solution, a white porcelain tile.
Procedure for the experiments:-
A variegated leaf plant is taken for this particular experiment to prove the necessity of chlorophyll for photosynthesis. A variegated leaf is a leaf in which different patches of colors are present in a Croton or Coleus or Geranium plant. The place where green patches are present in the leaf, chlorophyll pigment is present while at the other color patches present in the leaf contain other pigments but not chlorophyll. Before starting the experiment to prove chlorophyll is necessary for photosynthesis an important step has to be carried out is known as De-starching. De-starching is a step in which the starch present in the leaves of the plant will be removed by keeping the variegated leaves plant in a dark room or closed cup-board for about 48 hours. This step is done to ensure that previously synthesized starch in the leaves get consumed up because photosynthesis doesn't occur at that time as the plant is kept in dark place.
After De-starching step the variegated leaf plant is kept in bright sunlight for about 6 hours. After this one of the variegated leaf is plucked out from the experimental plant. Then Iodine test is conducted for this experimental leaf to find out whether the leaf prepared starch through photosynthesis or not.
A variegated leaf plant taken to prove chlorophyll is necessary for photosynthesis
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Steps to be followed for Iodine test:-
The plucked out experimental leaf is immersed in boiling water in the beaker for few minutes so that the cells of the leaf will be killed and at the same time metabolic activities of the leaf cells will be stopped.
Now the boiled leaf is taken out from the beaker with the help of a forceps. It is then placed in a test tube containing rectified spirit or ethanol. Then the leaf is boiled in ethanol over a water bath by keeping it in boiling water for about 10 minutes. The leaf dissolves its chlorophyll by boiling it in rectified spirit and then become pale-white.
Next the pale-white leaf is removed from the test tube by forceps and then it is washed in under warm water to make it soft.
Then this leaf is spread over a white porcelain tile and iodine drops were placed over at different parts of the leaf.
Result of Iodine test:-
Iodine is a purple colored reagent used to test the presence or absence of starch in the leaf conducted for photosynthesis process. In the presence of starch iodine solution will turn into blue-black color and in the absence of starch iodine added to leaf will turn into brown color.
In this experimental leaf, the part of the variegated leaf which contain green patches will give a positive test for starch i.e. iodine when added to this part of the leaf will turn into blue-black color. The reason for this is, this part of the experimental leaf containing green patches include chlorophyll and thus prepare starch through photosynthesis. Thus iodine added to this region will turn into blue-back color. But colored patches of variegated leaf doesn't include chlorophyll and thus don't prepare starch through photosynthesis. So iodine added in this region will change into brown color. Thus this experiment proves chlorophyll is necessary for leaves to prepare starch through photosynthesis.
Explanation:
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.