As you probably already know, plants are the primary food producers for all living organisms. Have you ever wondered how these green creatures produce food, not just for themselves, but for all living beings on this huge planet? The process through which green plants and a few other organisms produce their own food is called photosynthesis. The food produced by plants takes the form of glucose, the surplus of which is stored in fruits. Some plants might even store this surplus in their roots or stems. Other organisms then feed on these fruits, stems, and roots to gain energy for basic activities like cellular respiration. Therefore, while plants are called autotrophs, all other creatures that cannot produce their own food are termed heterotrophs. The photosynthesis process is the source of energy for all life forms.
Plants convert light energy into chemical energy through a series of chemical reactions which take place in the leaves in the case of green plants. These reactions from the photosynthesis cycle. You might also know that plants are the source of the oxygen gas which we breathe in. Oxygen too is produced during photosynthesis. The photosynthesis process involves capturing light energy by the plants and using it to convert carbon dioxide, water, and minerals available in the soil, into oxygen and organic compounds that are rich in energy. A close look at a photosynthesis diagram can help you get a better understanding of how light, water, and carbon dioxide are used by plants to produce oxygen, sugar compounds, and some carbon dioxide which is released into the air.
Photosynthesis: The Process
Photosynthesis is a chemical reaction involving the conversion of water, carbon dioxide, and minerals into glucose and oxygen by using light energy. It is an oxidation-reduction reaction. Oxidation refers to the removal of electrons from a molecule, while reduction is the process through which a molecule gains an electron. In the case of plant photosynthesis, light energy is used for the oxidation of water, producing oxygen gas, hydrogen ions, and some free electrons. Most of the removed electrons, along with the hydrogen ions are added to Carbon dioxide, reducing it to organic compounds. In most cases, carbohydrates like glucose, sucrose, and starch are the most significant organic products directly obtained from the photosynthesis process. This entire process occurs with the help of several enzymes that act as organic catalysts for the reaction to take place.
As mentioned previously, photosynthesis is a series of reactions that can broadly be divided into two different stages. These stages of photosynthesis are the “light” and the “dark” stages. The light stage consists of photochemical reactions, during which light energy is absorbed into the plant cells and used to conduct a set of electron transfers. The end products of this stage are adenosine triphosphate or ATP and nicotine adenine dinucleotide phosphate, or NADPH. Soon after, the dark stage begins during which the ATP and NADPH formed in the photochemical reactions are used for the reduction of carbon dioxide into organic carbon compounds. This process of generation of organic compounds from inorganic carbon is called carbon fixation.
The photosynthesis cycle depends on a large number of environmental and internal factors. The rate of photosynthesis can be determined on the basis of the oxygen rate production per unit weight of the aggregate chlorophyll present in the plant cells, or on the basis of oxygen production per unit mass of green plant tissues. This rate is dependent on factors like the amount of light available, the amount of carbon dioxide present in the air, the availability of water and minerals, and the average temperature. Each of these factors has to be available in the right amount, neither more nor less, for plants to be able to photosynthesize at a healthy rate.
The End Products of Photosynthesis
As you have already read, the reactants of photosynthesis make use of light energy to produce carbohydrates and oxygen. In the case of most green plant cells, among all the organic compounds produced directly during the process of photosynthesis, simple carbohydrates are the most important product. However, only a little amount of free glucose is produced in most plant cells. Instead, individual glucose units are joined together to form starch. In some cases, glucose is also linked with fructose, another form of sugar, to form sucrose. Contrary to traditional belief, plant photosynthesis does not generate only carbohydrates.
Proteins, amino acids, fats or lipids, and other components of green tissues are also produced during photosynthesis. The elements required to form these compounds are provided by minerals absorbed by the plant roots from the soil. These minerals include nitrogen, phosphorus, and sulfur. Gaseous oxygen is another important product of photosynthesis. Chemical bonds between carbon, hydrogen, oxygen, sulfur, and nitrogen are broken down and new bonds are created in the end products- gaseous oxygen and organic compounds. Breaking these bonds requires more energy than is released in the process of new bond formation. The surplus energy is therefore stored in the organic products, in the form of chemical energy.
The Importance of Photosynthesis
If you set mythology aside, heavenly beings did not bring life on earth, but plants and microorganisms who could photosynthesize did. In the grey barren world abundant with loose carbons and plenty of water, only plants could harness nature and build upon it. Earth neither had oxygen nor a suitable atmosphere that could bear life. Microorganisms and early plant lives that could perform photosynthesis started storing carbon in the form of carbohydrates and other polymer structures.
In return, they started to fill the atmosphere with oxygen. To this date, trees are the only organisms on earth that can convert carbon from the air into physical objects. Therefore, they are the primary source of all life on earth. The photosynthesis cycle makes life possible on earth, acting as the food source at all levels of the food chain. It was because of this process that plants and algae could store enough carbon under the surface of the earth, producing fossil fuels that run the world. These fossil fuels not only provide the energy required in factories, homes, and transportation systems but also act as the raw materials required for the manufacturing of plastics and other synthetic products. However, excessive use of fossil fuels is reversing the progress made in billions of years which had been facilitated by the photosynthesis process. This would soon render the earth uninhabitable again.
The process of photosynthesis is the chief source of food and oxygen on the planet earth and without this process, all forms of life would come to an end within no time. Plants are the only living organisms that produce oxygen through the process of cellular respiration, and hence they become absolutely irreplaceable in our ecosystem. No alternative to the process of photosynthesis has yet been found despite profound research in this field. However, the way human beings have been destroying nature, using up fossil fuels at the fastest rates possible, and cutting down trees in large numbers, it would soon become impossible for life to sustain on earth. If the earth is to survive, human beings have to ensure that the photosynthesis process never stops. This can be only when we decide to take care of the source of our very life through processes like reforestation and preservation of the natural resources.