write activity to show sunlight is necassery for photosynthesis
Answers
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.
Experiment for Sunlight is necessary for Photosynthesis
Sunlight is necessary for Photosynthesis experimental setup:- (Courtesy:-dev.elearn.punjab.gov.pk)
Procedure for the experiment
Before 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 leaf
By following steps Iodine test will be conducted for the experimental leaf:-
Steps to conduct Iodine Test
Steps to conduct Iodine Test:-(Courtesy:-dev.elearn.punjab.gov.pk)
First the experimental leaf is dipped in boiling water in the beaker for few minutes so that the cells of the leaf will be killed and metabolic process of the leaf cells will be stopped.
Now the boiled leaf in water is removed from the beaker with the help of a forceps and is placed in a test tube containing mentholated spirit. Then the leaf is boiled in mentholated spirit or ethanol over a water bath by keeping it in boiling water for about 10 minutes. The leaf looses its chlorophyll by boiling it in mentholated spirit and becomes pale-white.
Then the pale-white leaf is removed from the test tube and then it is washed in warm water to soften it.
Then this leaf is spread over a white porcelain tile and iodine drops are poured over at different places 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. 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.
