Experiment on Photosynthesis-Sunlight is necessary for Photosynthesis


Photosynthesis is a physiological process of green plants. One of the important factor required for photosynthesis is sunlight. In this resource I have explained in detail how an experiment can be conducted to prove the importance of the factor sunlight for this process. Along with the experiment I gave some important questions as well as answers related to the experiment which will be useful for those preparing for final practical or theory exams of various Boards.

Introduction

Photosynthesis 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.
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.
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

  • What is the aim of the above experimental set up?
    Ans. The aim of the above experimental setup is to prove that sunlight is essential for photosynthesis.
  • What is the first step done before starting of this experiment? What is the importance of this step?
    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.
  • What do you understand by the De-starching? How the leaves of plant will be De-starched?
    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.
  • Write the steps you follow to conduct Iodine test on the experimental leaf?
    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.
  • Why the experimental leaf was dipped in hot boiling water?
    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.
  • Why the leaf is boiled in mentholated spirit?
    Ans. To remove chlorophyll pigment from the cells of the leaf.
  • Why there is a difference in result of the iodine test in the covered and uncovered black paper regions of the experimental 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:-

Courtesy:-Youtube


Related Articles

How to conduct a Botany experiment on Photosynthesis

Photosynthesis is a physiological process of green plants. One factor that is more important for photosynthesis to occur is Carbon dioxide. In this resource I have explained in detail how an experiment can be conducted to prove the importance of the factor Co2 for this process. Along with this experiment I gave some important questions and answers related to the experiment which will be helpful for those preparing for year end practical or theory exams of various Boards.

How Oxygen is evolved by green plants in an experiment on Photosynthesis

Photosynthesis is an anabolic chemical process of green plants and it is a food synthesizing process. In this resource I have explained in detail how an experiment can be conducted to prove oxygen is evolved during photosynthesis process. Along with the experiment I gave some important questions as well as answers related to the experiment which will be useful for those preparing for final practical or theory exams of various Boards.

More articles: Botany Experiments

Comments

No responses found. Be the first to comment...


  • Do not include your name, "with regards" etc in the comment. Write detailed comment, relevant to the topic.
  • No HTML formatting and links to other web sites are allowed.
  • This is a strictly moderated site. Absolutely no spam allowed.
  • Name:
    Email: