Posted In: Biology

In Greek ‘photo’ means light and ‘synthesis’ means putting together. Photosynthesis is the process by which energy from sunlight is converted into chemical energy. Photosynthesis is performed by plants, algae and also certain bacteria. They take in water, carbon dioxide and light and make sugar which stores chemical energy. Oxygen is also released as a byproduct of this process.

Photosynthesis occurs during the day as plants need sunlight to produce energy and respiration happens as a continuous process. During night there is no sunlight and plants release carbon dioxide into the air.

Photosynthesis takes place in plant cell organelles called chloroplasts. They contain a green substance called chlorophyll. In plants, the light is absorbed by chlorophyll which is present in abundance in leaf cells. Chlorophyll absorbs the light energy of all colours except green for use in the photosynthesis process. The green colour light is reflected back by the plants resulting is the green colour characteristic of plants.

Photosynthesis | Image source:

The process of photosynthesis can be divided into two reactions

  • Light dependent reaction

This reaction takes place in the presence of light. Light from the sun is used to form energy carrying molecules.

  • Light independent reaction

It is also called the dark reaction. This can occur independent of light but it uses the chemical energy produced by the light reaction.

The photosynthesis equation
Photosynthesis is a process in which plants use the energy from the sunlight to produce sugar. The photosynthesis equation is the chemical representation of the process

Carbon dioxide + water → Glucose + oxygen
6CO2 + 6H2O → C6H12O6 +6O2

Six molecules of carbon dioxide plus six molecules of water produce one molecule of sugar and six molecules of sugar.

Plants get carbon dioxide form air through their leaves. There are small holes on the underside of leaves called stomata. Carbon dioxide enters through these stomata. There are loose fitting cells in the lower part of the leaf that allow the carbon dioxide to reach other leaves. This also allows the release of oxygen that is produced.

Leaves of plants have a large surface area and can thus absorb a lot of sunlight. The top surface of the leaf is protected from water loss and weather damage. Light falls on the surface of the leaf and it can absorb light as it has lot of chloroplast.

Plants get water which is needed for photosynthesis through their roots. Roots have big surface area with thin walls thus allowing the water to pass easily.

Why is photosynthesis important?
Photosynthesis causes an exchange of gases in the atmosphere. Plants take in carbon dioxide and give out oxygen as a by product. Thus, Photosynthesis plays a very important role in maintaining the oxygen content of the Earth’s atmosphere. All living beings need oxygen to survive. Photosynthesis decreases the content of carbon dioxide and other harmful industrial waste in the atmosphere that is a common cause of respiratory problems in human beings.

When animals and human beings consume plants in various forms, chemical energy stored in the plants is transferred to them. Photosynthesis can be considered as the ultimate source of life since it provides source of energy to animals and plants.

The glucose produced during the process is an energy unit and it helps plants to grow.



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