Тhe starting material for photosynthesis is atmospheric carbon dioxide and water. For the synthesis of organic substances, plants use only inorganic substances: nitrogenous, phosphorus, sulfur compounds. Molecules of atmospheric nitrogen also serve as a source of nitrogen, which bacteria that live in root nodules, mainly legumes, can fix. In this case, gaseous nitrogen passes into the composition of ammonia - NH4 and then enters into the composition of amino acids, proteins, nucleic acids and other compounds.
Organic substances that are formed in photosynthetic cells from carbon dioxide, water, atmospheric nitrogen and inorganic salts of the soil or aqueous media are used by all living things on our planet who are not capable of photosynthesis. These creatures include all animals and humans who live thanks to the energy of the sun transformed by plants. The exception is chemosynthetic microorganisms, which will be discussed below. Photosynthetic cells, capturing carbon dioxide from the atmosphere, release oxygen into it.
Before the appearance of photosynthetic cells and organisms on our planet, the Earth’s atmosphere was devoid of oxygen. With the advent of photosynthetic cells, it began to be saturated with oxygen. The gradual filling of the atmosphere with oxygen led to the appearance of cells with a new type of energy apparatus. These were cells producing energy due to the oxidation of organic compounds, mainly carbohydrates and fats, with the participation of atmospheric oxygen as an oxidizing agent.
The atmosphere created by photosynthesis protects the living from destructive short-wave UV radiation (oxygen-ozone screen of the atmosphere). Only 1-2% of solar energy goes into the crop of agricultural plants, losses are due to incomplete absorption of light. Therefore, there is a huge prospect of increasing yields due to the selection of varieties with high photosynthesis efficiency and the creation of a crop structure favorable for light absorption. In this regard, the development of the theoretical foundations of photosynthesis control and the study of photosynthesis as an integral process become especially relevant.
Photosynthesis is the main entry of inorganic carbon into the biological cycle. All free oxygen in the atmosphere is of biogenic origin and is a by-product of photosynthesis. The formation of an oxidizing atmosphere (oxygen catastrophe) completely changed the state of the earth's surface, made possible the appearance of respiration, and in the future, after the formation of the ozone layer, allowed life to land.
Photosynthesis, which is one of the most common processes on Earth, determines the natural cycles of carbon, oxygen and other elements and provides the material and energy basis of life on our planet. Photosynthesis is the only source of atmospheric oxygen.
