Photosynthesis of plants and its features

Photosynthesis of plants is a complex physico-biochemical process, through which plants convert electromagnetic energy in the sun to chemical energy used in organic compounds. This process is based on a chain of oxidation-reduction chemical reactions, as a result of which electrons are transferred from the donor-reducing agents, which are hydrogen and water, to acceptors that are oxidizers. In this case, carbohydrates are formed and O2 is released during the oxidation of water.

Photosynthesis of plants has two consecutive stages. The first stage is called light (photochemical). At this stage, the quantum light energy is converted into chemical energy for the connections of high-energy compounds, and also into a universal reductant. In the second stage, called the dark (metabolic), the resulting chemical energy and the universal reductant undergo a cycle to fix and restore carbon dioxide, resulting in the formation of carbohydrates. The mechanism of photosynthesis divides the light and dark stages not only in time, but also in space. The light stage passes in special thylakoid energy-converting membranes, while dark reactions pass either in the stroma of the chloroplast or in the cytoplasm.

Photosynthesis and respiration of plants is based on the absorption of light quanta, where the main role is played by chlorophylls, the absorption spectrum of which includes the visible region, as well as the parts of infrared and ultraviolet regions nearest to it. The main pigment for all plants that perform photosynthesis is chlorophyll a. Green algae, mosses and vascular plants also have chlorophyll b, which expands the absorbed light spectrum. Some species of algae also contain chlorophylls c and d. In addition to chlorophylls, carotenoids and phycobilins also take part in the absorption of light.

After the absorption of light, a photochemical stage begins, in which two photosystems of types I and II (PS1 and PS2) take part. Each of the photosystems consists of a reaction center where charges are separated, the electric transport chain where the electrons are oxidized, and a set of components that perform processes for photo-oxidation of water and regeneration of the reaction center. In reaction centers, the quantum light energy is converted into chemical, and then the electrons move according to the gradient of the electrochemical potential, which is an electron transport chain of photosynthesis.

The photosystem of type II performs reactions on photooxidation of water, as a result of which oxygen and a proton of H + are formed. In parallel to the photosynthetic transport of electrons, a process of proton transfer from the chloroplast to the intralithicoid region occurs. As a result of the reactions, NADPH and ATP are formed, which are the primary products of photosynthesis. Further photosynthesis of plants forms enzymatic reactions in which from carbonic acids proteins, carbohydrates and fats are obtained. If the dark metabolism has a non-carbohydrate orientation, then amino acids, organic compounds and proteins are formed.

Metabolic processes by the type of CO2 fixation are divided into C3-, C4- and CAM-photosynthesis. Carbohydrates, which are formed during the dark stage of photosynthesis, can be deposited in chloroplasts as starch compounds, come out of chloroplasts to form new cells, and serve as a source of energy for metabolic reactions.

Photosynthesis of plants uses only 1-2 percent of the absorbed light energy. The intensity of the photosynthetic process is affected by the spectral composition and intensity of light, temperature, water regime of the plant and its mineral nutrition, the concentration of CO2 and O2, as well as other environmental factors.