Posted In: Biology

Photosynthesis is the process by which plants take in carbon dioxide and water and use sunlight as a source of energy to produce glucose and oxygen. In addition to plants, algae and certain bacteria also perform photosynthesis.

Process of photosynthesis step by step

For photosynthesis to occur three elements are required:

1. Light - Photosynthesis takes place inside plant cells called chloroplasts. Chloroplasts contain a green substance called chlorophyll. Chlorophyll absorbs light for photosynthesis to happen.
2. Carbon dioxide - Plants get carbon dioxide from air through their leaves. It diffuses through the stomata that are small holes in the underside of the leaf.
3. Water - Water required for photosynthesis is obtained from the roots of plants.

Photosynthesis | Image source:

Photosynthesis happens during the day when there is sunlight. The process of photosynthesis can be divided into two parts:

  • Light dependent reaction (Light reaction)

This reaction requires sunlight to produce the organic energy molecules (ATP and NADPH). Photosynthesis increases with more light as more chlorophyll molecules are ionised and more energy molecules are generated.

  • Light independent reaction (Dark reaction)

This reaction uses energy molecules produced by the light reaction to produce more energy molecules.

Did you know: Photosynthesis is one of the most important chemical processes on Earth.

The process of photosynthesis

The process of photosynthesis step by step is as follows:

  • Photosynthesis takes place in the leaves of the plants. Chlorophyll in the leaves absorbs sunlight. Carbon dioxide enters the leaves from the air through stomata. The water comes from the roots of plants.
  • During the day light dependent reactions occur. During this process water is divided into hydrogen and oxygen ions. The electrons then go through a series of electron carriers that leads to the accumulation of hydrogen ions. In this way, energy molecules ATP and NADPH are formed.
  • The dark reaction converts carbon dioxide to glucose using the energy produced during the light reaction. The conversion of carbon dioxide to glucose requires a series of reactions. The same molecule produces glucose during the process. This series of reaction begin and end with the same molecule and is called the Calvin cycle.  
  • The lower part of the leaf has loose fitting cells. This structure allows carbon dioxide to reach the other leaves and also facilitates easy release of oxygen generated during photosynthesis.

The photosynthesis equation
Photosynthesis can be represented by the following chemical equation:

6CO2 + 6H2O + light energy → C6H12O6 + 6O2
Carbon dioxide + water + light energy →glucose + oxygen

The condition required for photosynthesis
Photosynthesis depends on light. Only visible light range from blue to red is considered good for the photosynthesis process. This is because Chlorophyll reflects green light and absorbs red and blue light.

Ultraviolet light and infrared light are not suitable as the former has too much energy and the latter does not have enough energy.

The presence of particles in water can affect the amount of light that reaches the water. More the presence of particles in water, lesser will be the amount of light that can penetrate. Without sufficient light the photosynthesis process will decrease.

The temperature of water also affects the photosynthesis process. This process speeds up with heat. The effect of temperature on photosynthesis depends on the species of algae and bacteria. Each organism has a different optimum temperature range.


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