IntroductionPhotosynthesis is an important physiological activity of green plants. For photosynthesis to occur in green plant the factors required are Sunlight, Chlorophyll and Carbon dioxide. To prove the necessity of these factors there are certain specific experiments have to be in the laboratory. So students must know clearly how a particular experiment will be done for each factor clearly and also must realize why a particular step will be done for the success of the experiment with reasons.
Aim of the experiment:-To prove Sunlight necessary for green plants to prepare their food.
Requirements:-A well watered potted green plant, two strips of black papers, small clips, spirit lamp or bun sen burner, test tube, beaker, Petr-dish, water, mentholated spirit or rectified spirit or ethanol, iodine solution.
Sunlight is necessary for Photosynthesis experimental setup:- (Courtesy:-dev.elearn.punjab.gov.pk)
Procedure for the experimentBefore starting the experiment to prove Sunlight is necessary for photosynthesis an important step has to be carried out is known as De-starching. De-starching is a process in which the starch present in the leaves will be eliminated by keeping the plant in dark room or closed cup-board for about 48 hours. This step is done to ensure that previously manufactured food in the leaves get consumed when the plant was kept in dark place since photosynthesis doesn't occur at that time.
Next strips of black paper will be arranged one on either side of the selected leaf of the De-starched plant with the help of clips. Now the whole plant is kept in bright Sunlight for about 3-4 hours. Then the strips of black papers are removed from the experimental leaf and then starch test or Iodine test is conducted for the experimental leaf.
How to conduct starch test on the experimental leafBy following steps Iodine test will be conducted for the experimental leaf:-
Steps to conduct Iodine Test:-(Courtesy:-dev.elearn.punjab.gov.pk)
Result of Iodine testIodine is a purple colored reagent used to test the presence or absence of starch in the leaf conducted for photosynthesis process. When iodine test is conducted for the experimental leaf, the leaf where black paper was covered will turn into brown color and the part of the leaf which is not covered with black paper will turn into blue-black color. This result clearly indicates starch is formed in the leaf where sunlight is available and starch is not formed where the leaf doesn't got the sunlight as it is covered by black paper.
Here is an Experiment on Transpiration-More transpiration occurs from lower surface of a dicot leaf than upper
Questions and answers related to the experiment
Ans. The aim of the above experimental setup is to prove that sunlight is essential for photosynthesis.
Ans. Before starting of this experiment De-starching of the leaves of the plant to be done. This step will be done to ensure that there is no starch in the leaves of the experimental plant.
Ans. De-starching is the elimination of starch from the leaves of an experimental plant by keeping it in dark room for about two days.
Ans. Write the four steps mentioned above under the heading "How to conduct starch test on the experimental leaf" and also mention the result of iodine test.
The experimental leaf was dipped in hot boiling water to kill the cells of the leaf so that the metabolic process of the cells of the leaf will be stopped.
Ans. To remove chlorophyll pigment from the cells of the leaf.
Iodine test in the black paper uncovered region show a positive result for the presence of starch i.e iodine in this region turns into blue-black color. The reason for this is that uncovered region gets sunlight and so this part of the leaf is able to synthesize starch.
The black paper covered region give a negative result for starch i.e. iodine in this region turns into brown color. The reason for this is black paper covered region gets no sunlight and so this part of the leaf is not able to synthesize starch.
Here is a video on this experiment:-
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