Significance of Photosynthesis in Plants: Notes for NEET 2022 Biology

Overview

Photosynthesis is a widely used term in biology. In this process, the conversion of light energy into a good amount of chemical energy has been done with the help of prototrophs. This converted energy can be useful to fuel the cellular activities in plants. 

The converted chemical energy is being stored in sugars, which are created by carbon dioxide and water. 

In this article, we will deeply discuss how photosynthesis works for plants and other related concepts while understanding their significance.

Photosynthesis – Definition

In simple words, photosynthesis is the process by which plants utilise sunlight, carbon dioxide and water to produce oxygen and a good amount of energy in the form of sugar. 

From the definition, it can be understood that the process is exclusively taken place in the chloroplasts through photosynthetic pigments, namely chlorophyll b, xanthophyll and carotene etc.

Photosynthesis has been utilised by all green plants and fewer other autotrophic organisms to produce nutrients with the help of carbon dioxide, sunlight, and water. The end product of photosynthesis is oxygen.

Importance of photosynthesis

Not only to greener plants but photosynthesis can also be applied to other organisms. This means that it would also include prokaryotes, namely cyanobacteria, green sulphur, and purple bacteria. These organisms have the ability to exhibit photosynthesis the same as compared to green plants. 

The glucose produced during the process of photosynthesis can be useful in fuelling various other cellular activities. The product of this physio-chemical process is oxygen. This can be represented using the following equation,

Carbon dioxide+water+sunlight → Glucose+oxygen

• Algae can also use photosynthesis to transform solar energy into chemical energy. Here, oxygen gas is being liberated as its by-product, while light is considered a major factor in this process.
• Photosynthesis happens when plants utilise sunlight to convert carbon dioxide and water into oxygen and glucose. The leaves of the plants consist of microscopic cellular organelles called chloroplasts. 
• Every chloroplast consists of a green coloured pigment known as chlorophyll. Here light energy can be absorbed by the chlorophyll molecules while oxygen is entered through the tiny pores of stomata situated in the epidermis of leaves.
•  Some of the other by-products of this process are glucose and fructose.
• The above-produced sugar molecules are sent to the stems, roots, seeds, flowers, leaves and roots. In simple words, these sugars are used as an energy source by plants. This will help them grow.
• Furthermore, these molecules can combine to form more complex carbohydrates such as starch and cellulose. Cellulose is nothing but a structural material that can form cell walls in plants.

Where does this process take place?

Chloroplasts act as a site of photosynthesis in green plants and blue-green algae. All the greener parts of the plants, including sepals, green leaves, green stems, and floral plants, consist of chloroplasts, which are nothing but green colour plastids. All these cell organelles are contained only within the plant cells and can be located in the mesophyll cells of leaves.

Factors affecting photosynthesis

The photosynthesis process has been affected by a number of factors. Below mentioned are some of them:

• Temperature

The temperature range should be between 25 and 35 degrees Celsius for the execution of the photosynthesis process to be effective.

• Intensity of light

The rate of photosynthesis depends on the intensity of the light. The more intense the light is, the higher the rate of photosynthesis. Meanwhile, when the intensity of the light is low, the rate of photosynthesis is also lower.

• Water

Water is one of the most fundamental requirements to generate photosynthesis. Whenever there is a lack of water, photosynthesis is low. Water scarcity leads to problems such as the intake of carbon dioxide. The deficiency of water will lead to the refusal of the opening of stomata to retain the amount of water they have stored.

• Pollution

There are high chances that the pollution caused by industries and other similar wastes might settle on the surface of the leaves. This will lead to the blockage of stomata pores and make the carbon dioxide intake process much slower. 

• The concentration of C0₂

To increase the rate of this process, the concentration amount of carbon dioxide should be higher as well. Moreover, the required amount of carbon dioxide should be at least in the range of 300 to 400 PPM.

Equation of photosynthesis

There are only two reactants involved in this process: water and carbon dioxide. These two reactants produce two useful products, namely glucose and oxygen. Therefore, the photosynthesis process is considered an endothermic reaction. Given below is the equation (or formula) of photosynthesis:

6 CO2+6 H2O → C6 H12 O6+6 O2

Contrary to plants, certain bacteria which perform this process do not produce oxygen as their by-product. Such types of bacteria are termed as anoxygenic photosynthetic bacteria. Meanwhile, those who do produce oxygen as a by-product of photosynthesis are named as oxygenic photosynthetic bacteria.

Photosynthetic pigments

Leaves contain several types of pigments. The following are the four major types:

1. Chlorophyll a
2. Chlorophyll b
3. Xanthophylls
4. Carotenoids

Structure of chlorophyll

Chlorophyll is a type of green pigment that can be easily found in the chloroplasts of a plant cell and the mesosomes of cyanobacteria. This greenish pigment is involved in the photosynthesis process by allowing plants to absorb energy from sunlight. Chlorophyll a and chlorophyll b combine to form chlorophyll. 

Apart from green plants, other such organisms could perform photosynthesis and have various other forms of chlorophyll, namely chlorophyll c1, chlorophyll c2, chlorophyll f and chlorophyll d.

Process of photosynthesis

The process of photosynthesis occurs in two stages namely,

• Light reaction or light dependent reaction
• Dark reaction or light independent reaction

Light reaction

• In plants, the light reaction can take place in the thylakoid membranes of chloroplasts.
• The grana, which is nothing but membrane-bound sacs like structure contained inside the thylakoid, functions by forming light and is named photosystems.
• These photosystems contain huge complexes of pigments and molecules of proteins present among the plant cells. Moreover, they take up a primary role during the light reactions of photosystems.
• The two types of photosystems are photosystem I and photosystem II.
• Under the light-dependent reactions, there are high chances that the light energy can be easily converted into ATP and NADPH, which can be seen utilised in the 2nd phase of photosynthesis.
• ATP and NADPH can be created with the help of two-electron transport chains during light reactions. Here water is predominantly used while producing oxygen as the product.

The following is the reduced chemical equation:

2 H2 O+2 NADP+3ADP+3Pi → O2+2NADPH+3ATP

Dark reaction

• Another name for the dark reaction is the carbon fixing reaction.
• Dark reaction is a light-independent process where the sugar molecules are available to be formed with carbon dioxide and water molecules.
• This light-independent reaction can occur in the stroma of the chloroplast, where the utilisation of NADPH and ATP products has been done.
• Plants can capture the carbon dioxide from the atmosphere through stomata and are being delivered to the Calvin photosynthesis cycle.
• The formation of NADPH and ATP during the light reaction drives the reaction in the Calvin cycle. This helps convert six carbon dioxide molecules into one molecule of glucose.

Below mentioned is the chemical equation for dark reaction:

3 CO2+6 NADPH+5 H2O+9 ATP → G3P+2H+ 6 NADP+9 ADP+8 Pi

Importance of photosynthesis

• Photosynthesis is the most fundamental thing for a living organism to survive in this world. It is very important for all the lives on earth. Moreover, it also serves a crucial role in the food chain because the plants create their food with the help of photosynthesis, thereby generating primary producers.
• Another main feature of producing photosynthesis is that it produces oxygen as one of its by-products, which is essential for any organism to survive in this world.

Interesting facts:

The given below are some of the most common yet surprising facts about photosynthesis:

• The reverse process of photosynthesis is cellular respiration.
• Plants are not the only living organisms that utilise photosynthesis.
• The colour of the leaves will be subjected to change during autumn because plants slow down the photosynthesis process.
• Molecules of glucose combine to form more complex molecules used by plants.
• Plants consist of specialised tissues that aid photosynthesis.
• For 1 molecule of glucose to be formed during photosynthesis, there involve six molecules of carbon dioxide and six molecules of water.
• The 1st stage of photosynthesis involves capturing energy from the sun to break down water molecules.
• The Calvin cycle is regarded as the 2nd stage of photosynthesis.
• Grana and stroma are the two main parts of a chloroplast.
• The leaves of plants are greenish due to chlorophyll in it.

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