What is Photosynthesis? and Its Importance in plant



Photosynthesis and Its Importance

One of the main characteristics of living things is their ability to feed. This is called nutrition. Both plants and animals feed. While some organisms called autotrophs can manufacture their own food through a process called photosynthesis other organisms called heterotrophs cannot. Both plants and animals need food for energy supply.


Also Read: Root System: Definition, Types and Functions

What is Photosynthesis?

Photosynthesis is process in which green plants, algae, and cyanobacteria utilize the energy of sunlight to manufacture carbohydrates from carbon dioxide and water in the presence of chlorophyll. 

Some of the plants that lack chlorophyll, e.g., the Indian pipe, secure their nutrients from organic material, as do animals, and a few bacteria manufacture their own carbohydrates with hydrogen and energy obtained from inorganic compounds (e.g., hydrogen sulfide) in a process called chemosynthesis. However, the vast majority of plants contain chlorophyll—concentrated, in the higher land plants, in the leaves.

In these plants water is absorbed by the roots and carried to the leaves by the xylem, and carbon dioxide is obtained from air that enters the leaves through the stomata and diffuses to the cells containing chlorophyll. 

The green pigment chlorophyll is uniquely capable of converting the active energy of light into a latent form that can be stored (in food) and used when needed


Importance of photosynthesis in Plant

Photosynthesis plays a vital role in our environment. The whole life form is directly or indirectly dependent on the process of photosynthesis carried out by plants. If photosynthesis does not occur in plants then plants cannot synthesize the food. 

This causes the imbalance in the environment. The plants will not produce oxygen and then no animal life will be able to survive due to the absence of oxygen. 

We will not get oxygen, food, and life on this planet will be extinct. Photosynthesis is very important both to plants and animals for the following reasons.

1. Production of Food: Photosynthesis provides food for both plants and animals. All green plants are able to manufacture their food through the process of photosynthesis while animals depend directly or indirectly on the green plant for their food.

2. Purification of the Atmosphere: Waste products like carbon(IV)oxide released during respiration by both plants and animals is removed from the atmosphere by plants for use during photosynthesis.

3.  Release of Oxygen to the Environment: Oxygen needed for respiration by plants and animals is released into the environment during photosynthesis.

4. It serves as building blocks for other substance: Photosynthesis provides the building block or carbon skeleton on which other food substances such as proteins, fats, oil etc are built.


Also Read: Flowering Plants: Structure and Characteristics

Mechanism of Photosynthesis

Photosynthesis is an endothermic reaction and it consists of a series of complex reactions. These reactions during photosynthesis are grouped into two stages called Light reaction and Dark reaction.

Light Reaction Stage Light reaction stage occurs during the day or in the presence of sunlight. The light energy or solar energy is captured by the chlorophyll and electrons are excited. The energy so trapped is used to split water into hydrogen ion (H) and hydroxyl ion (OH). This splitting of water into hydrogen ion (H) and hydroxyl ion (OH) is called photolysis of water.

During this process, oxygen is given out as by-product as shown in the Chemical equation above. At the same time, a compound, co-enzyme or NADP is reduced by hydrogen ion to NADPH and ATP (Adenosine Triphosphate) is formed.


Dark Reaction Stage

Dark reaction occurs at night or in the absence of light. Together with the energy provided by ATE: the reduced compound Nicotinamide Adenine Dinucleotide (NADP) then lead to the assimilation of carbon dioxide. Through a series of steps, each controlled by a specific enzyme, a three carbon compound (CH20) or sugar is formed.


Materials and Conditions Necessary for Photosynthesis

For photosynthesis to take place, certain materials or conditions must be available. These are carbondioxide (carbon (IV) oxide), water, chlorophyll, sunlight, mineral salt, suitable temperature and enzymes these factors are external except for chlorophyll and enzymes which are internal factors necessary for photosynthesis to take place.

1. Carbon (IV) oxide: Carbon(IV)oxide is derived from the atmosphere and it diffuses into the intercellular spaces through the stomata of the leaves. From the intercellular spaces, carbon (IV)oxide diffuses further into the mesophyll cells containing chloroplast.

2. Water and Mineral salts: Water and mineral salts are derived from the soil. They pass into the roots of plants through the root hairs by a process called Osmosis. Water and dissolved mineral salts are conducted by xylem from the roots through the stem and finally to the mesophyll cells containing chlorophyll of the leaves.

3. Sunlight: Sunlight is obtained from solar energy. The light from the sun is trapped by the chlorophyll of the leaves. The sunlight is used to split water into hydrogen ion and hydroxyl ion in a process called Photolysis.

4. Optimum Temperature: Temperature is derived partly from the solar energy and partly from chemical reactions within the leaves druing which heat is generated. Suitable temperature is important for enzymes to enable them function properly during photosynthesis.

5. Chlorophyll: Chlorophyll is the green colouring pigment found in the pallisade and spongy mesophyll of the leaves. The chloroplyll represents sites where food can be synthesized and it helps to trap solar energy and convert it to chemical energy.

The Photosynthetic Process

The initial process in photosynthesis is the decomposition of water (H2O) into oxygen, which is released, and hydrogen; direct light is required for this process. The hydrogen and the carbon and oxygen of carbon dioxide (CO2) are then converted into a series of increasingly complex compounds that result finally in a stable organic compound, glucose (C6H12O6), and water.

This phase of photosynthesis utilizes stored energy and therefore can proceed in the dark. The simplified equation used to represent this overall process is 6CO2+12H2O+energy=C6H12O6+6O2+6H2O. In general, the results of this process are the reverse of those in respiration, in which carbohydrates are oxidized to release energy, with the production of carbon dioxide and water.

The intermediary reactions before glucose is formed involve several enzymes, which react with the coenzyme ATP to produce various molecules. Studies using radioactive carbon have indicated that among the intermediate products are three-carbon molecules from which acids and amino acids, as well as glucose, are derived. This suggests that fats and proteins are also products of photosynthesis.

The main product, glucose, is the fundamental building block of carbohydrates (e.g., sugars, starches, and cellulose). 

The water-soluble sugars (e.g., sucrose and maltose) are used for immediate energy. The insoluble starches are stored as tiny granules in various parts of the plant—chiefly the leaves, roots (including tubers), and fruits—and can be broken down again when energy is needed. Cellulose is used to build the rigid cell walls that are the principal supporting structure of plants.

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