Experiments Related to Photosynthesis: Definition & Demonstration

Experiments Related to Photosynthesis: Green plants exhibit an autotrophic mode of nutrition. We all know that leaves are the site of photosynthesis. Leaves possess chlorophyll that traps the sunlight to synthesise food (glucose) by utilising inorganic raw materials, i.e., carbon dioxide and water. Oxygen is released as a by-product of photosynthesis. The glucose units combine and form a complex carbohydrate called the starch that remains stored in the plant cells for further utilisation.

Different experiments related to photosynthesis can be performed to demonstrate the utilisation of carbon dioxide, involvement of chlorophyll, presence of starch, and release of oxygen by the plant leaf subjected to perform photosynthesis. Let’s read the article to study the detailed procedure of different experiments related to photosynthesis.

What is Photosynthesis?

Photosynthesis is the process by which the chlorophyll-containing cells synthesise food (glucose) from carbon dioxide and water in the presence of sunlight. Photosynthesis is the process of conversion of solar energy into chemical energy.

Chloroplasts – The Site of Photosynthesis

The leaves are the parts of plants that participate in the process of photosynthesis. In herbaceous plants, green and flexible stems also perform photosynthesis. The mesophyll cells of leaves contain chloroplasts that possess a green coloured pigment called chlorophyll to trap the sunlight for photosynthesis. Thus, inside the mesophyll cells of leaves, chloroplasts are the site of photosynthesis.

Events Occuring During Photosynthesis

The following events occur during the process of photosynthesis:

1. Absorption of water from the soil through root hairs.
2. Diffusion of Carbon dioxide through stomata.
3. Absorption of light energy by chlorophyll.
4. Production of glucose.
5. Conversion of glucose into starch.
6. Release of oxygen

Conditions Necessary For Photosynthesis

The following conditions are necessary for photosynthesis:

1. Sunlight
2. Chlorophyll
3. Carbon dioxide
4. Water

The effect of the presence and absence of these factors on the process of photosynthesis can be proved by performing certain experiments related to photosynthesis.

Experiments to Demonstrate the Requirement of Materials for Photosynthesis

1. Theoretical Demonstration for the Requirement of Chlorophyll During Photosynthesis:

I. Aim: Chlorophyll is a green coloured pigment that traps the sunlight to proceed with the synthesis of food by leaves by utilising carbon dioxide and water. To demonstrate the requirement of chlorophyll in photosynthesis, the following experiment is performed.

II. Materials required: Variegated leaf, water, alcohol, iodine solution.

III. Procedure:
a). Take a plant with variegated leaves: The leaves of the Coleus, Croton plant can be taken. The leaves of these plants have yellow and green patches, and The green patches contain chlorophyll.
b). Destarching the plant: The plant is placed in a dark room to prevent photosynthesis and thereby allows the plant to utilise the food that is stored in the form of starch.
c). Removal of chlorophyll: The leaf is boiled in the water, followed by boiling of leaf in the alcohol (place the beaker containing alcohol and leaf in a water bath) till it becomes pale white, i.e., the chlorophyll is removed, and the alcohol turns green. The leaf is then washed with warm water so that it becomes soft.
d). A few drops of iodine solution are poured over the leaf.

IV. Observation: The green coloured portion of the leaf that turns colourless in the alcohol now turns into blue-black patches after putting the iodine, while the yellow-coloured portion of the leaf does not show any colour change.

V. Conclusion: The results obtained from the iodine test prove that chlorophyll is necessary for the process of photosynthesis. The blue-black colour is due to the presence of starch. As in the yellow portion, no photosynthesis takes place, so there is no colour change due to the addition of iodine.

Fig: Experiment to demonstrate the necessity of chlorophyll for photosynthesis

2. Theoretical Demonstration for the Requirement of Sunlight During Photosynthesis:

I. Aim: All living beings utilise energy for several life processes. Likewise, plants utilise light energy for the process of photosynthesis. The requirement of sunlight can be demonstrated by following the below-mentioned steps:

II. Materials required: Green plant, black paper or aluminium foil, water, alcohol, iodine solution.

III. Procedure:
a). Destarching the plant
The plant can be destarched naturally by placing it in the complete dark for about 2-4 days so that all the stored starch is utilised by plants to fulfil its food and energy requirement in the absence of photosynthesis.
b). Covering one of the leaves with black paper
The destarched plant is then placed in the sunlight for about 2-4 days by covering any of its leaves with black paper or aluminium foil. Since the black colour absorbs the maximum amount of sunlight and therefore obstructs the pathway of light to the leaf surface, therefore black paper is used to cover the leaf.
c). Boiling of covered leaf in water
The covered and uncovered leaves are immersed in the boiled water before testing for the starch because immersing the leaf in boiled water breaks down the cell membranes of the mesophyll cells and makes the leaf more permeable to the iodine solution.
d). Removal of chlorophyll
Since chlorophyll interferes in the test for starch due to its green colour, therefore it is necessary to remove the chlorophyll to get the appropriate findings of the experiment. Chlorophyll removal involves the boiling of leaf in water then into alcohol and further washed with hot water to soften it.
e). Test for the starch
The covered and processed leaf is further tested for the presence of starch by adding 2-3 drops of iodine on the leaf surface.

III. Observation: It will be observed that the leaf does not show any colour change. However, an uncovered leaf gives a positive result for the presence of starch by changing its colour to blue-black.

IV. Conclusion: This shows that the leaves that are exposed to sunlight could only perform photosynthesis, while the covered leaf could not perform photosynthesis due to the absence of sunlight.

Fig: Experiment demonstrating the necessity of sunlight

3. Theoretical Demonstration for the Requirement of Carbon Dioxide During Photosynthesis

I. Aim: Carbon dioxide is the waste product of respiration that is utilised in the process of photosynthesis. To demonstrate the requirement of carbon dioxide the following steps are performed:

II. Material required: Two green potted plants, bell jar, alcohol, water, potassium hydroxide, iodine solution.

III. Procedure:
a). Destarching of plant
Plants can be destarched by keeping them in the dark for about 2 days. In this experiment, two destarched plants are taken.
b). Designing the artificial boundaries for plant
The two plants are individually placed on separate glass plates and are covered separately with a bell jar to restrict their boundaries within the surrounding area.
c). Role of potassium hydroxide
Potassium hydroxide is a carbon dioxide absorbent. It is placed with any of the potted and covered plants that absorb the carbon dioxide in its vicinity. The setup should be airtight to ensure to restrict the further entry of carbon dioxide in the jar.
d). Removal of chlorophyll
The chlorophyll interferes in the test for starch due to its green colour. Therefore it is necessary to remove the chlorophyll from the leaves of both plants to get the appropriate findings of the experiment. Chlorophyll removal involves the boiling of leaf in water then into alcohol and further washed with hot water to soften it.
e). Test for the presence of starch
Both the experimental setup are tested for the presence of starch by putting 2-3 drops of iodine solution on the leaf of both plants from which the chlorophyll has been removed.

III. Observation: It has been observed that the leaf of the plant that is placed in the bell jar along with potassium hydroxide will not show any colour change, while the other placed alone in the bell jar shows the presence of starch in its leaves by turning the colour into blue-black.

IV. Conclusion: Since the potassium hydroxide crystals absorb the available carbon dioxide present in one of its jars, therefore photosynthesis does not occur. This proves that carbon dioxide is necessary for photosynthesis.

Fig: Experiment demonstrating the necessity of carbon dioxide

Experiment to Demonstrate the Production of Substances in Photosynthesis

1. Theoretical demonstration for the presence of starch

I. Aim: Plants utilise inorganic raw materials, i.e., water and carbon dioxide, to synthesise organic materials called glucose. These glucose units combine to form a complex carbohydrate called starch that remains stored in the stroma of the chloroplast and in the cytoplasm of the leaves. The iodine test is prominently performed to test the presence of starch that is discussed as follows:

II. Material required: Green plant, iodine solution, dropper.

III. Procedure:
a). The healthy plant is placed in the sunlight and left undisturbed for about one day before this experiment.
b). Now, the chlorophyll is removed from the leaf by boiling the leaf in water then into alcohol and further washed with hot water to soften it.
c). The leaf of the plant is then tested for the presence of starch by adding 2-3 drops of iodine solution with the help of a dropper to the leaf surface.

III. Observation: It will be observed that the colour of the leaf turns blue-black.

IV. Conclusion: The blue-black colour ensures the presence of starch and therefore ensures that photosynthesis takes place in the leaf.

2. Theoretical Demonstration for the release of oxygen during photosynthesis

I. Aim:  Plants release oxygen during photosynthesis that is utilised in the process of respiration. To ensure the release of oxygen, the following steps should be followed:

II. Material required: An aquatic plant, sodium bicarbonate, water, beaker, funnel.

III. Procedure:
a). Design the experimental setup
A beaker full of water is taken, and any aquatic plant such as Hydrilla is placed at the bottom of the beaker. The plant is further covered with the inverted funnel. An inverted test tube is placed over the funnel.
b). Plant subjected to perform photosynthesis
The experimental setup is then placed in the sunlight to facilitate the process of photosynthesis to occur in the plant. Sodium bicarbonate is added to the water to provide carbon dioxide that is needed for photosynthesis.
c). Observation: A number of air bubbles can be observed at the top closed end of the test tube. Since there is no place for the oxygen to escape from the inverted test tube.
IV. Conclusion: The presence of bubbles ensures that oxygen is released during photosynthesis. We can test for the presence of oxygen bubbles by taking a glowing splinter in contact with the air bubbles.

Fig: Experiment demonstrating the release of oxygen

Summary

Photosynthesis is the process of synthesising food by utilising carbon dioxide and water in the presence of sunlight. The leaves are the kitchen factories of the plant as they contain chlorophyll in their mesophyll cells to absorb the sunlight. The importance of chlorophyll can be tested by using variegated leaves that show only green patches of the leaves can absorb sunlight since they contain chlorophyll and perform photosynthesis. On the other hand, if a small portion of the entire green leaf is covered with black paper, it does not perform photosynthesis due to the absence of sunlight.

The presence of starch can be confirmed by performing an iodine test. The release of oxygen can be tested by taking an aquatic plant placed in a water-filled beaker along with the inverted funnel and test tube that are placed one after another over the plant and later tested for the release of oxygen. By studying these experiments, we came to know about the importance of carbon dioxide, sunlight, and water in a plant for photosynthesis. These experiments also ensure the type of food synthesised by plants and the release of life-supporting gas.

Frequently Asked Questions (FAQs) On Experiments Related to Photosynthesis

Q.1. Why only Hydrilla is used in photosynthesis experiments?
Ans: Hydrilla is a small, aquatic plant that is easy to handle and able to breathe in the water, therefore used in the demonstration of the release of oxygen during photosynthesis.

Q.2. How can we destarch the plant?
Ans: We can destarch the plant by keeping the plant in the dark for about one to two days.

Q.3. How do you decolourise the leaf?
Ans: We can decolourise then placing it into a beaker containing alcohol and boiling the leaf in a water bath.

Q.4. How do you test the presence of starch in a leaf?
Ans: The presence of starch can be tested by putting 2-3 drops of iodine on the leaf. If the colour turns blue-black, it ensures the presence of starch in the leaf.

Q.5. Which experiment proves that carbon dioxide is essential for photosynthesis?
Ans: Moll’s half-leaf experiment proves that carbon dioxide is essential for photosynthesis.

We hope this detailed article on experiments related to photosynthesis helped you in your studies. If you have any doubts, queries or suggestions regarding this article, feel to ask us in the comment section and we will be more than happy to assist you. Happy learning!