Step 1: Carbon dioxide in the atmosphere enters the plant leaf through stomata, i.e., minute epidermal pores in the leaves and stem of plants which facilitate the transfer of various gases and water vapor.
Step 2: Water enters the leaves, primarily through the roots. These roots are especially designed to draw the ground water and transport it to the leaves through the stem.
Step 3: As sunlight falls on the leaf surface, the chlorophyll, i.e., the green pigment present in the plant leaf, traps the energy in it. Interestingly, the green color of the leaf is also attributed to presence of chlorophyll.
Step 4: Then hydrogen and oxygen are produced by converting water using the energy derived from the Sun. Hydrogen is combined with carbon dioxide in order to make food for the plant, while oxygen is released through the stomata. Similarly, even algae and bacteria use carbon dioxide and hydrogen to prepare food, while oxygen is let out as a waste product.
The electrons from the chlorophyll molecules and protons from the water molecules facilitate chemical reactions in the cell. These reactions produce ATP (adenosine triphosphate), which provides energy for cellular reactions, and NADP (nicotinamide adenine dinucleotide diphosphate), essential in plant metabolism.
The entire process can be explained by a single chemical formula.
While we take in oxygen and give out carbon dioxide to produce energy, plants take in carbon dioxide and give out oxygen to produce energy.
Photosynthesis has several benefits, not just for the photoautotrophs, but also for humans and animals. The chemical energy stored in plants is transferred to animals and humans when they consume plant matter. It also helps in maintaining a normal level of oxygen and carbon dioxide in the atmosphere. Almost all the oxygen present in the atmosphere can be attributed to this process, which also means that respiration and photosynthesis go together.