From Big Medical Encyclopedia

ASSIMILATION in biology (Latin. assimilatio likening, identification) — process of assimilation by an organism of the substances coming to it from the environment as a result of which these substances become a component of live structures or are postponed in an organism in the form of stocks. And. and dissimilation provide continuous updating of organic matter throughout all life of an organism. Intensity And. and its ratio with dissimilation is varied both at various organisms, and throughout life of one individual. Most intensively And. occurs in growth periods: at animals — at young age, at plants — during the vegetative period.

Assimilation at animals — see. Metabolism and energy .

Assimilation at plants. Many chemical elements, first of all With, Oh, Η, N, R, S, K, Mg, Sa, and microelements enter into composition of the substances forming biomass of plants and participating in processes of life activity: Fe, Cu, Mo, Μη, In, Co, Zn, etc. Plants acquire them from the environment in molecular composition of inorganic or organic matters, or in the form of ions of mineral salts, subject to various transformations and involve them in processes of life activity.

On a way of assimilation of basic elements (first of all carbon) plants divide into two groups: heterotrophic and autotrophic (see. Autotrophic organisms , Heterotrophic organisms ).

Heterotrophic plants can acquire carbon only as a part of organic matters and receive energy at partial (fermentation) or full (breath) their oxidation. This majority of bacteria, mushrooms deprived of a chlorophyll the highest plants parasites.

Autotrophic plants absorb carbon in the form of carbon dioxide gas. In this case full assimilation of carbon requires its inclusion in molecular composition of synthesizable organic matters with turning into got into condition. Expenses of energy from external sources and special mechanisms of its use are for this purpose necessary. Autotrophic plants have such mechanisms. Heterotrophs, without possessing such mechanisms, are forced to eat the ready organic compounds containing the energy necessary for life activity.

Photoautotrophic green plants carry out process of synthesis of organic compounds by means of the energy of light absorbed by verditer green — a chlorophyll (see. Photosynthesis ). The essence of photosynthesis consists in recovery of carbon of carbonic acid by means of the hydrogen received from water. The first stage of photosynthesis — oxidation of water by means of energy of light. At the same time oxygen is emitted from water, and the electrons and protons of hydrogen enriched with energy are used for formation of high-energy chemical compounds (see Visokoergichesky connections). The energy which is in them participates in the subsequent reactions proceeding in the dark. At the same time at a final stage the difficult recovery pentozofosfatny cycle (Calvin's cycle) therefore end products of photosynthesis are formed, first, (carbohydrates) is carried out and, secondly, regenerates an acceptor of CO 2 — ribulezodifosfat. Products of photosynthesis are also organic acids, amino acids, proteins, lipids and pigments (in particular, a chlorophyll). In different conditions and at various conditions of plants the players of products of photosynthesis are changed that testifies to its important regulatory role in processes of life activity.

Carbon dioxide gas of free air is a source of carbon for geophytes. Water plants use the dissolved carbon dioxide gas and carbonates. During intensive photosynthesis and growth geophytes on the area of 1 hectare can assimilate within a day more than 160 kg of carbon, forming at the same time up to 600 — 700 kg of organic matters and connecting apprx. 800 — 1600 thousand kilocalories of energy of a sunlight. During vegetation it makes 2500 — 6000 kg of carbon, 6000 — 15 000 kg of organic matters and 24 — 60 million kilocalories of energy. Green plants of the globe assimilate annually about 40 billion sink carbon, forming apprx. 100 billion tons of organic matters, connecting about 400 X 1015 kcal of energy and allocating 120 billion tons of oxygen in the atmosphere.

Some green and purple bacteria also acquire carbon by means of energy of light, but use not water, but hydrogen sulfide, hydrogen and other connections for recovery of carbonic acid. At the same time free oxygen is not emitted. Such way of assimilation of carbon is called a photoreduction.

A number of not green microorganisms assimilates carbon and hydrogen and forms organic matters of carbon dioxide gas and water not due to energy of light, and due to energy of oxidation organic (e.g., methane) or inorganic (e.g., H 2 S, Fe ++ , N 2 etc.) substances. Such way of assimilation of carbon and synthesis of organic matters is called chemosynthesis.

Not green heterotrophic plants (bacteria, mushrooms, parasites from among the higher plants) acquire carbon in the form of ready organic matters from which the best material are sugar. Other nitrogen-free substances, apparently, especially are suitable for food of a certain microorganism, than easier they can be turned in simple sugar. So, polyatomic alcohol and oxyacids are especially favorable for mold mushrooms, and substances with a straight carbon chain are processed easier than their isomers with a branched chain.

The substances deprived of the oxidized carbon atoms (hydrocarbons) for the majority of organisms bad or in general unsuitable nutritious material. However a number of microorganisms is capable to use also these connections. On it industrial receiving fodder and food proteinaceous biomass as a result of growth of culture of microorganisms is based on some fractions of oil refining and combustible natural gases. At assimilation of carbon in the form of ready organic matters heterotrophic organisms subject their usually most part to full oxidation, scooping from this energy necessary to them. Therefore life activity of heterotrophic organisms is connected with a decrease of the general reserves of organic matters. Maintenance of life on Earth requires systematic replenishment of these stocks, as carry out autotrophic organisms. In life activity of plants

assimilation of nitrogen is important. The higher plants acquire nitrogen generally in the form of ions of NO 3 or NH 4 + and partially as a part of organic compounds. The nitrogen acquired in the form of NH 4 + , reacts with ketonic acids, forming amino groups of amino acids (see. Nitrogen metabolism , Amino acids ). Nitrogen in the form of NO 3 is exposed to recovery. The amine formed at the same time a hydroxyl, reacting with ketonic acids, aminates them with formation of amino acids; the last are included proteins. Some lowest organisms are capable to assimilate molecular nitrogen from air, previously fixing it and transferring to composition of organic compounds (nodule bacteriums, free living nitrogen-fixing bacteriums and some blue-green seaweed). The nitrogen connected thus or directly, or after a number of transformations (mineralization) becomes available to the higher plants (see. Nitrogen , a nitrogen cycle in the nature).

Sulfur is acquired by the higher plants in the oxidized state in the form of SO4-anions, but is exposed to recovery and is entered in a row organic compounds in the form of disulfide (— S — S —) or sulphhydryl (— S — N) groups. Such connections play an important role in redoxreactions.

Phosphorus assimilates in the form of salts orthophosphoric to - you and is a part of a number of complex proteins, phospholipids, nucleic acids, etc. Forming phosphoric ethers with an organic compound series, phosphoric to - that plays an extremely important role in exchange and transformation of substances: activates them (e.g., carbohydrates), provides transfer of energy from a respiratory cycle on implementation of biosintez and other vital processes.

Potassium, calcium, magnesium are acquired in the form of ions of salts and perform the most various functions: are a part of some important connections (e.g., Mg — structure of a chlorophyll or some enzymes), play a role of specific catalysts of some processes, support a certain mode of the intracellular environment and a condition of biocolloids and membranes, neutralize some organic acids (e.g., oxalic acid) etc.

See also Dissimilation .

Bibliography: Kondratyeva E. H. Photosynthesizing bacteria, M., 1963, bibliogr.; Kretovich V. L. Fundamentals of phytochemistry, M., 1971; M and sh at with - oozes E. N and Shilnikova V. K. Biological fixing of atmospheric nitrogen, M., 1968; Nichiporovich A. A. Light and carbon food of plants — photosynthesis, M., 1955; Pryanishnikov D. N. Nitrogen in life of plants and in agriculture of the USSR, M. — L., 1945; Rabinovich E. Photosynthesis, the lane with English, t. 1 — 3, M., 1951 — 1959.

A. A. Nichiporovich.