As the name photosynthesis suggests, it is a chemical process by which light energy, especially solar energy, is used by plants as well as some other organisms to convert carbon dioxide (CO2) into various organic compounds. Chlorophyll present in the plants and other organisms work to convert the inorganic substances into organic substances in the presence of light. These organic substances are used as food by these plants and other organisms.
Plants, algae as well as some bacteria groups are capable of undertaking photosynthesis. However, it does not occur in archaea. All organisms that are capable of photosynthesis are known as "photoautotrophs". It is worth mentioning here that all organisms that utilize light as the source of energy for undertaking photosynthesis do not use carbon dioxide (CO2) as their carbon source. Such organisms are called "photoheterotrophs" and they make use of organic substances as their source for carbon for undertaking photosynthesis.
During the photosynthesis process, plants, algae as well as cyanobacteria use carbon dioxide (CO2) and water, while water and oxygen are released as a waste product. In fact, photosynthesis is crucial for survival of life on Earth. This is because photosynthesis not only helps to maintain the normal oxygen level in the atmosphere, but nearly all forms of life on the Earth are also directly dependent on it as an important source of energy or indirectly as the definitive energy source in the food they consume.
During this chemical process, plants absorb carbon dioxide and water both from the atmosphere and soil. Once water taken up by the roots from the soil enters the plant cells, it is oxidized. In other words, water loses its electrons. On the other hand, carbon dioxide (CO2) is reduced - in other words, it gains electrons. As a result of this water is transformed into oxygen, while carbon dioxide turns into glucose. Subsequently, plants give out the oxygen into the atmosphere, while storing the energy inside the glucose molecules.
The process of photosynthesis begins when a chlorophyll molecule in the plant leaf takes up a minute light packet (known as photon). The plant uses the photon’s energy to move an electron in the chlorophyll to an elevated orbit as a result of which the electron progresses to another molecule. Such donation of an electron is called energy input which kicks off an entire series of chain reactions.
The process of photosynthesis can be separated into two steps. While a number of the reactions take place in the presence of light, there are others that happen in the absence of light. The first reaction is completely on light; that is when the chlorophyll absorbs a photon to move an electron. The removal of an electron from the chlorophyll molecule actually triggers a chain of complex reactions that result in the production of molecules which detains light energy and stocks it up in the form of adenosine triphosphate (ATP). The cells of the plant tap into this amassed energy or ATP and provide the force required for the essential life processes.
The next step is not dependent on light. In other words, this part of the reaction takes place in the dark. In this part, the adenosine triphosphate (ATP) molecules that are stored in plant molecules are utilized to trigger another series of complex reactions that are known as the Calvin Cycle. This reaction assists the plants to utilize carbon dioxide (CO2) obtained from the air and water taken in by the roots from the soil to produce glucose for their food. Though we say that the second step of photosynthesis does not require light, the fact is that ATP production as well as the light and dark reactions would come to a halt if light did not exist.
Photosynthesis is of great importance to all living organisms as without it we would be lacking the basic life force making it impossible for us to live. When we consume plants or animals that feed on plants, we actually store glucose (which is an energy) obtained from these foods till this energy is released during cellular respiration.
Our cells absorb glucose from the foods we eat and oxygen that we take in from the air. During the photosynthesis process, the plants mainly produce energy (glucose) for their food, while oxygen and water (the two important by-products of photosynthesis) are released by them. Therefore, plants not only provide us with glucose for our energy, but they also release oxygen that we breathe. While plants are capable of making their own food and growing, they also require us, especially for carbon dioxide that we produce during cellular respiration. While plants release oxygen during the photosynthesis process as a by-product, they require carbon dioxide we produce for their energy as well as formation of new cells.
It is worth mentioning here that plants have a fundamental role in helping to continue life on the Earth via the photosynthesis process. Several elements including food and energy, atmospheric gasses, wood and other side products, petroleum products and medicinal products help the plants to achieve this. A brief description of each of these is presented below.
Atmospheric gases: During the photosynthesis process, plants absorb carbon dioxide (CO2) and give out oxygen, which is a by-product. Without photosynthesis life would not have been possible on the Earth. In fact, photosynthesis helps to maintain the normal balance of oxygen in the atmosphere and in the absence of the photosynthesis process the amount of oxygen would deplete rapidly as humans and animals use this gas for respiration. Moreover, several activities like combustion also use oxygen. On the other hand, the level of harmful carbon dioxide would go to dangerous levels in the absence of photosynthesis. Therefore, we may conclude that photosynthesis helps to maintain a normal balance of these two vital gases in the atmosphere.
Food and energy: All green plants having chlorophyll make their own food via photosynthesis. Such plants are known as producers. On the other hand, humans and animals are consumers since they get all their food requirements directly or indirectly from plants. Precisely speaking, plants directly provide more than 80% of the food requirement of the greater part of the world's population. The animals obtain the remaining part of their food requirement from other animal sources. In fact, animals are also a part of the food chain that begins with the plants. When we talk about the food chain, the energy we receive from the foods we consume is in fact a product of the process called photosynthesis irrespective of whether the food has been obtained from plants or animals.
Petroleum products: Most of us would be surprised to learn that our car runs on the energy that was light energy once. Even the cooking gas we use at home or restaurants is actually a product of the photosynthesis process. In fact, the petroleum we get now is actually the light energy stored by plants in their system many millions of years ago. That light energy has been converted to petroleum due to the animals that consumed those plants. The light energy was eventually converted into petroleum owing to the powerful pressure on these plants as well as animals for millions of years and more. In fact, coal as well as natural gas also has been produced in the same manner.
Wood and other side products: Photosynthesis also gives us various other products either directly or indirectly. Wood is used for a variety of purposes, which includes combustion and construction. Moreover, wood is also needed to make paper. All these plant products are direct products of photosynthesis. Similarly, several natural fibers, including cotton, comprise cellulose that is almost entirely virtually produced when plants undertake photosynthesis. Wool is obtained from sheep, which, in turn, obtains its food from plants. Hence, it can be safely concluded that even the clothes we wear comes from photosynthesis.
Medical products: It is worth mentioning here that majority of the medicines are produced using a variety of chemicals hauled out of plants. In fact, it has been confirmed that thousands of plants possess medicinal properties. For instance, aspirin is draw from salicylic acid, which is obtained from the willow tree's bark. A popular analgesic, aspirin is also used to reduce formation of blood clots, especially in patients with heart disease.
Aside from aspirin, more potent painkillers like morphine and codeine are manufactured from opium. Then again, opium is actually the extract of poppy plants. Currently, scientists are continuing with experiments to establish the therapeutic properties of several other plant species, particularly the plants that grow in the tropical rainforests. Keeping this aspect in view, it is very important that we need to protect as well as preserve the natural habitats of all such valuable plant species.