Experiments to Show Photosynthesis

In previous classes, and in this class too, you will read about numerous experiments to show photosynthesis took place in a plant. There is a long list of such experiements and hence it can be confusing to remember them. I will try to explain these experiments in simplest possible way.

You have read that once carbohydrate is made in leaves, it is changed into starch so that it can be stored. So, all the experiments related to photosynthesis try to show the presence of starch. Presence of starch implies that photosynthesis took place in a particular plant. You may recall that when starch reacts with iodine, it makes a complex which is dark blue in colour. This test it done in all these experiments to show the presence of starch.

In these experiments, two samples are tested. Factor of photosynthesis is ruled out in one sample, and this factor is allowed to remain in another sample. After that, leaves from both the samples is boiled in alcohol over water bath. This results in denaturation of leaf, i.e. removal of chlorophyll from leaves. After that, the boiled leaf is washed and then iodine drops are poured over it. Formation of dark blue colour indicates the presence of starch.

You can look for pictures of variegated leaves for example. A leaf which has spots of many colours apart from green is called variegated leaf. Spots with colours other than green do not have chloroplast in them. So, photosynthesis does not happen in those portions of leaf. The green portions will turn dark blue in this experiment, showing photosynthesis took place in green portions.

Significance of Photosynthesis:

Photosynthesis is the main way through which the solar energy is made available for different living beings.
Green plants are the main producers of food in the ecosystem. All other organisms directly or indirectly depend on green plants for food.
The process of photosynthesis also helps in maintaining the balance of carbon dioxide and oxygen in the air.
Green plants play dual role in ecosystem. One of the roles is of producer, i.e. converting solar energy into food so that other organisms can survive on this planet. The second role is of keeping the environment in healthy shape, by maintaining the balance between oxygen and carbon dioxide in atmosphere.