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Photosynthesis as a Life Process

Updated on July 9, 2015

Living forms have some basic processes which help in the survival and perpetuation of race called life processes. Photosynthesis one of it where green plants synthesis carbohydrates utilizing external factors like sunlight and CO2 and internal factors like water and chloroplasts, in leaves which are the main sites of photosynthesis. Oxygen is liberated in this process, which makes our living possible.
Roger Bacon, known as the founder of experimental science said "Doing experiments for yourself is the way to learn about nature". Trying to experiment whenever, you can, helps a lot in enhancing your scientific attitude.

Set your mind and let yourself enter into the world of Biology to learn more, to attain longterm retention so that you can gain success.
Photosynthesis is a photochemical reaction where plants utilise Sunlight, CO2, Chloroplasts, Water, Enzymes, Mineral salts etc., to prepare their own food (Carbohydrates).
Photosynthesis as a process:
We can't see anything without light. It is a form of energy. Plants use this energy to prepare food by utilising other factors necessary.
We often feel that the water we pour to the plants is the source of food for them. But water is one of the factors of photosynthesis.

The nutrient chemicals in the water are transformed to carbohydrates with the help of chlorophyll in the leaves. The water from the land is sucked (absorbed) and transported to all parts of the plant through the stem, by the roots.
Leaves absorb CO2 from the environment, with the help of sunlight, they split CO2 to carbon and oxygen. They combine nutrients with carbon to prepare carbohydrates.
Even though a plant has green leaves, nutrients, CO2 it can't prepare food in the absence of any other factor also (like CO2, chlorophyll, water).

It is estimated that approximately 150-200 tons of carbon element is used by the leaves every year during photosynthesis.
Whatever may be the food item (rice, pulses, vegetables, fruits, nuts etc.,) we use in food (which come from plants) is prepared by photosynthesis.
Thus leaves are considered as food factories of the plant.

The overall equation of photosynthesis:

Here, utilizing the light energy, simple compounds are transformed to new compound. Lets see:

Why are the leaves green in colour ?

The young leaves are light red in colour and they change into green colour after few days. Why? When anything absorbs or reflects the colours of the sunlight, it get its colour.

Chlorophyll and carotene are the two pigments present in leaves. The leaf look green due to chlorophyll and yellow due to carotene. The colour of the leaf changes according to the ratio of these two substances (pigments). Very young leaves have red coloured pigment called anthocinin, thus, they look red. In due time, chlorophyll and carotene are produced and then the colour of the leaf is changed. When sunlight falls on the leafs, except green colour (from 7 VIBGYOR colours) all the other six colours are absorbed and green is reflected. Thus, we can see leaves in green colour. Leaves without chlorophyll cannot prepare food on their own.

Importance of O2:


Plant kingdom is giving life to us by releasing O2. In the absence of O2, there will be no life on earth. O2 was first recognised by Lavoiser Preistly. It is a colourless, tasteless, odourless gas. Even plants breath oxygen at nights.

Liberation of O2 during photosynthesis is demonstrated by using Hydrilla plant:
You have to take a few healthy twigs of Hydrilla. Keep them in a funnel and invert the funnel in a beaker of water. Then you have to invert a test tube over the stem of the funnel,and leave the setup in sunlight for sometime. Bubbles will be seen rising up in the test tube after sometime.
Then you have to insert a glowing splinter deep into it by removing the test tube carefully. What will you see? you will see the splinter burning brightly.

Now just ask yourself these questions and answer them.
1. What is the gas collected in the test tube due to the downward displacement of water?
2. Why is it that oxygen is evolved in this experiment?
Answers :
1. Because the splinter glows very brightly, we can say that the gas collected is oxygen.
2. As the Hydrilla twig carries out the process of photosynthesis, it absorbs CO2 and releases O2.
So, by this experiment we know that:
1) Oxygen is produced during photolysis of water in the light phase of photosynthesis during which molecular oxygen is released into the atmosphere for reuse of respiration.

2) Due to the liberation of oxygen, that the splinter burnt so brightly

  • The leaf is the main site of photosynthesis. Its broad thin lamina is an adaption for this purpose.
  • Water, a raw material in the soil, travels to the leaf from the roots via the xylem.
  • CO2, a raw material in the air, enters the leaf through stomata on the lower surface of the lamina.
  • Sunlight which is absorbed by chloroplasts in the leaf, provides the energy for photosynthesis.
  • Glucose is a high - energy product of photosynthesis. It travels to all parts of the plant through the phloem.
  • Oxygen, a waste product of photosynthesis, leaves the leaf through stomata on the lower surface of the lamina.

Lets Know about a scientist:

Jan Ingen housz :

  • He was a Dutchman who studied Physics, Chemistry and Medicine.
  • He was one of the first people to study photosynthesis.
  • He followed up the discovery by Joseph Priestley (1733-1804) that plants give off oxygen and later published a work on gas exchange in plants.
  • He showed that the green part of plants take in carbondioxide and release oxygen when sunlight falls on them.
  • He has also shown that the opposite happens in the dark.


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