PHOTOSYNTHESIS

Schematics of Photosynthesis in Plant

Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms' activities (energy transformation).

The word photosynthesis can be separated to make two smaller words:

• Photo which means light
• Synthesis which means putting together

In simple words, "Photosynthesis is the process by which plants make their own food".

The raw material required for the process of Photosynthesis are as follows:

• Carbon dioxide
• Water
• Sun Light

1. Carbon Dioxide:

• Carbon dioxide is present as a gas in the atmosphere; hence by the process of diffusion, the terrestrial (land) plants get CO₂ through their stomata.
• Some amount of carbon dioxide is also present in the soil in the form of carbonates that is also absorbed by the plants along with water.
• However , the aquatic plants that are submerged in water absorb carbon dioxide in gaseous form from water, which is very challenging as the rate of gaseous diffusion is very low in water. 
• Hence, as an adaptive mechanism, many submerged plants, such as various form of algae and angiosperms, use bicarbonates from the water to obtain carbon dioxide for photosynthesis.

2. Water :

• Water is another inorganic ingredient that is required for photosynthesis. 
• The oxygen released as a by-product in photosynthesis comes from water molecules only. 
• The plants on land directly absorb water from the soil through their roots.
• In case of aquatic plants, the water is available in large amounts for the freshwater plants; but for saltwater plants, salt becomes a problem. When water enters, salt also penetrates with it and cause the water to leach out from the plant. Hence, these plants generally have thick waxy leaves and stems that do not allow the penetration of salt.

3. Light :

• The process of photosynthesis requires light energy that plants obtain by absorbing the light through their green colored pigment called chlorophyll. Thus, the presence of chlorophyll is very essential for photosynthesis.
• The green color of the plant or any plant part indicates the presence of chlorophyll and its ability to do photosynthesis.
• Chlorophyll absorbs most of the energy from all parts of the white light spectrum (VIBGYOR) except the green part, which is reflected back.

Chlorophyll :

• It is a complex organic compound composed of carbon, hydrogen, oxygen, nitrogen, and magnesium. There are eight types of chlorophyll molecules; however, the most common ones are chlorophyll a and b.
• Further, there are accessory pigments  that absorb the energy, which is not absorbed by the chlorophyll, and they are called Carotenoids;  on the other hand, the pigment that absorb blue light and give yellow, orange, and red color to the respective plant parts are called Anthocyanins. 
• A non-green plant or a plant with non-green leaves does not imply that it cannot photosynthesize. This is due to the presence of high amounts of other pigment that cover the green color of the chlorophyll. For example, purple leaves of tradescantia and red Japanese maple. 
• The plant that are white in color and completely lack pigment cannot photosynthesize.
• Since large amounts of chloroplasts are present in the leaves, they are considered as the photosynthetic organ of the plant.

Although the process of photosynthesis takes place in  step, the overall process can be represented in the form of the given chemical equation: