For the normal functioning of the cell and the entire multicellular organism, the constancy of the internal environment is necessary, which is called homeostasis.
Homeostasis is the constancy of the internal environment of biological systems.
Homeostasis is supported by metabolic reactions, which are subdivided into assimilation (anabolism) and dissimilation (catabolism). All reactions occurring in the cell are aimed at maintaining homeostasis, this requires substances and energy.
The whole set of reactions of biosynthesis of substances and their subsequent assembly into larger structures, going with the expenditure of energy, is called assimilation, anabolism or plastic metabolism.
Plastic metabolism includes photosynthesis, biosynthesis of proteins, nucleic acids, fats and carbohydrates. Assimilation processes are especially intensive in the growing cells of the developing organism.
Energy is needed to carry out plastic metabolism. The cell receives it from the decomposition reactions of organic compounds stored or obtained from the outside. With the participation of enzymes, these substances decompose into simpler compounds; in this case, energy is released, part of which is released in the form of heat, and part is stored in the form of ATP molecules. If necessary, the energy of ATP is used to compensate for the energy costs of the cell, for example, to ensure assimilation processes.
The set of reactions of decomposition of substances, accompanied by the storage of energy, is called dissimilation, catabolism or energy metabolism.
Assimilation and dissimilation are opposite processes: in the first case, the formation of substances occurs, for which energy is spent, and in the second, the decay of substances with the formation and storage of energy.
Assimilation and dissimilation are two sides of a single process of metabolism and energy in the cell, which is called metabolism.
Metabolism (metabolism) is a set of interrelated processes of synthesis and breakdown of chemicals in the body.
Assimilation and dissimilation are always strictly balanced and coordinated, and a violation of this balance leads to the development of a disease of both individual cells and the whole organism, or even to their death.