Learn About Photosynthesis, Definition, Equation - Embibe
• Written By Manisha Minni
• Written By Manisha Minni

# Photosynthesis: Process, Equation and Factors

Photosynthesis Process: Photosynthesis is the process by which a plant converts light energy into chemical energy for the production of food. A plant uses water, carbon dioxide, and sunlight in the presence of chlorophyll to produce food or energy in the form of sugar and releases oxygen as a by-product. The word “Photosynthesis” is broken into two words, Photo means ‘Light‘ and Synthesis means ‘To Put Together. Humans, along with other animals, are dependent on plants for survival. Plants and algae produce the oxygen we need for survival, as well as the carbohydrates we need for energy. These things are all produced through photosynthesis.

In this article, we will talk about the process of Photosynthesis, factors and the equation of Photosynthesis. Let us know more about the process of Photosynthesis that helps sustain life on earth with the help of sunlight, water and carbon dioxide.

## Photosynthesis: Definition

Photosynthesis is a physicochemical process in which autotrophs convert light energy into chemical energy to synthesise organic compounds, which are stored in the form of sugar and later used to complete cellular activities. In this process, carbohydrates and oxygen are synthesized by using carbon dioxide and water in the presence of sunlight. The word Photosynthesis is derived from the Greek word, “Photo” means “light”, and “Synthesis” means “putting together”. To sum up, this word means “combining together with the help of light.”

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### Photosynthesis Equation

Fig: Chemical Reaction of Photosynthesis

### Sites of Photosynthesis

Chloroplasts are the cell organelle that carries out Photosynthesis in plants. Every green part of a plant, including the green stems, green leaves, take part in Photosynthesis. The mesophyll cells of leaves have many chloroplasts that hold specialised light-absorbing green pigments called chlorophyll. The chloroplasts are known as the kitchen of the cell because complete food synthesis takes place here.

Fig: Chloroplast

### Photosynthetic Pigments

Photosynthetic pigments are light-absorbing molecules, which absorb only specific wavelengths of visible light but reflect others. The photosynthetic pigments are of two types based on their significance.

1. Primary Pigments: The pigment forms the main molecule of the photosystem, e.g., Chlorophyll a and Chlorophyll b.
2. Accessory Pigments: These support the function of primary pigments, e.g., Xanthophylls and Carotenoids.

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The reaction centre contains Chlorophyll a molecule where the energy is trapped. The antenna pigments are mainly chlorophyll b, xanthophylls and carotenoid molecules, which absorb photons and transfer their energy to the reaction centre.

Fig: Photosynthetic Pigments

### Process of Photosynthesis

Photosynthesis takes place in two main phases. These are light-dependent and light-independent phases.

A. Light-dependent Phase

1. In this phase, light plays the main role.
2. The light reaction takes place in the thylakoids of the chloroplast.
3. Activation of chlorophyll- The chlorophyll on exposure to light energy becomes activated by absorbing photon particles.
4. Splitting of water- In the activated chlorophyll in the presence of sunlight, $${{\rm{H}}_{\rm{2}}}{\rm{O}}$$ breaks down into $${{\rm{H}}^{\rm{ + }}}$$ and $${\rm{O}}{{\rm{H}}^{\rm{ – }}}$$ and releases electrons. This reaction is known as photolysis of water which means splitting by light.
5. Formation of NADPH- NADP (Nicotinamide adenine dinucleotide phosphate) is known as Hill reagent. The hydrogen ions $$\left( {{{\rm{H}}^{\rm{ + }}}} \right)$$ are picked up by a compound NADP to form NADPH.
6. Evolution of oxygen- The oxygen $$\left( {\rm{O}} \right)$$ component is given out as molecular oxygen $$\left( {{{\rm{O}}_{\rm{2}}}} \right){\rm{.}}$$
7. Photophosphorylation- In the activated chlorophyll, in the presence of sunlight, ADP and Pi combine together to form energy-rich compound ATP. This is called photophosphorylation. These can be of two types cyclic and non-cyclic photophosphorylation.
8. So, the net production of light reaction will be ATP, $${\rm{NADPH + }}{{\rm{H}}^{\rm{ + }}}$$ and $${{\rm{O}}_{\rm{2}}}{\rm{.}}$$

B. Light-independent Reaction or Dark Reaction or Biosynthetic Phase

1. In this phase, light is not required.
2. This occurs simultaneously with the light reaction.
3. This occurs in the stroma of the chloroplast.
4. The hydrogen of NADPH is used to combine with $${\rm{C}}{{\rm{O}}_{\rm{2}}}$$ by utilising ATP energy to ultimately produce glucose $$\left( {{{\rm{C}}_{\rm{6}}}{{\rm{H}}_{{\rm{12}}}}{{\rm{O}}_{\rm{6}}}} \right){\rm{.}}$$
5. This fixation of $${\rm{C}}{{\rm{O}}_{\rm{2}}}$$ is catalysed by the enzyme Rubisco (Ribulose bisphosphate carboxylase).
6. This fixation of $${\rm{C}}{{\rm{O}}_{\rm{2}}}$$ occurs in a number of steps using a special $${\rm{C}}{{\rm{O}}_{\rm{2}}}$$ acceptor compound RUBP (Ribulose bisphosphate).
7. During the dark reaction of photosynthesis carbon of $${\rm{C}}{{\rm{O}}_{\rm{2}}}$$ is absorbed and assimilated into glucose. So the process of dark reaction is known as carbon assimilation.

Fig: Light Dependent and Light-Independent Phase

### Factors of Photosynthesis

There are many external and internal factors that affect Photosynthesis.
1. External Factors
a. Light– The rate of Photosynthesis is directly proportional to the intensity of light.
b. Carbon dioxide– Initially, carbon dioxide increases the rate of Photosynthesis, but after optimum level, it acts as a reducing factor.
c. Water– Increased water availability causes a steady increase in the rate of Photosynthesis.
d. Temperature– The rate of Photosynthesis increases with an increase in temperature. The optimum temperature for Photosynthesis is $${\rm{35 – 4}}{{\rm{0}}^{\rm{0}}}{\rm{C}}{\rm{.}}$$ After that, the rate decreases with the increase in temperature.

2. Internal Factors
a. Chlorophyll– The rate of Photosynthesis increases with increased chlorophyll content.
b. Structure of leaf– The thickness of the cuticle, the distribution of stomata, and the size of the leaf influence the rate of Photosynthesis.

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#### Significance

The significance of Photosynthesis are mentioned below:
1. Photosynthesis is a physicochemical process that is an utmost source of breathable oxygen in the air.
2. In the food chain, plants are the primary producer, and they create their food using Photosynthesis.
3. Photosynthesis helps in the purification of air.
4. The relationship of photosynthesis to man is important not only from the standpoint of food but also from the point of economic existence and civilization.

#### Summary

Photosynthesis is the process by which a plant converts light energy into chemical energy for the production of food. A plant uses water, carbon dioxide, and sunlight in the presence of chlorophyll to produce food or energy in the form of sugar and releases oxygen as a by-product. Chloroplasts include chlorophyll and other light-sensitive pigments that catch solar energy. The photosynthetic cells can transform this solar energy into organic molecules that carry energy, such as glucose, in the presence of carbon dioxide. These cells not only maintain the global carbon cycle but also generate much of the oxygen present in the atmosphere.

Q.1. What are the different stages of Photosynthesis?
Ans:
There are two stages of Photosynthesis:
i) Light-dependent or photochemical reaction
ii) Light-independent or Dark reaction or Biosynthetic Phase

Q.2. What is photosynthesis?
Ans:
Photosynthesis is the process by which carbohydrates (glucose or other sugar) and oxygen are synthesized by using carbon dioxide and water in the presence of sunlight.

Q.3. What is Calvin Cycle?
Ans:
Calvin Cycle takes place in the stroma of the chloroplasts. This is also referred to as the light-independent reaction.

Q.4. Mention different types of photosynthetic pigments?
Ans:
There are 4 major photosynthetic pigments present in chloroplasts. These are Chlorophyll a, Chlorophyll b, Xanthophylls and Carotenoids.

Q.5. Where do the light-dependent and light-independent reactions of Photosynthesis take place?
Ans:
Light-dependent reaction takes place in the thylakoid membranes of chloroplasts, and the light-independent reaction takes place in the stroma of the chloroplasts.

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