1. The molecular level. The molecular level carries separate, albeit significant, signs of life. At this level, an amazing uniformity of discrete units is revealed. The basis of all animals, plants and viruses are 20 amino acids and 4 of the same bases that make up the nucleic acid molecules. In all organisms, biological energy is stored in the form of energy-rich adenosine triphosphoric acid (ATP). The hereditary information of all is embedded in the molecules of disoxyribonucleic acid (DNA), capable of self-reproduction. Realization of hereditary information is carried out with the participation of ribonucleic acid (RNA) molecules.
2. The cell level. The cell is the main independently functioning elementary biological unit, characteristic of all living organisms. In all organisms, only at the cellular level are biosynthesis and realization of hereditary information possible. The cell level in unicellular organisms coincides with the organism level. There was a period in the history of life on our planet (the first half of the Proterozoic era ~ 2000 million years ago), when all organisms were at this level of organization. Such organisms consisted of all species, biocenoses and the biosphere as a whole.
3. The fabric level. A collection of cells with the same type of organization is tissue. The tissue level arose with the advent of multicellular animals and plants having different tissues. The great similarity between all organisms remains at the tissue level.
4. Organ level. Jointly functioning cells belonging to different tissues make up the organs. (Only six main tissues are part of the organs of all animals and six main tissues form organs in plants).
5. Organizational level. At the body level, an extremely large variety of forms is found. The variety of organisms belonging to different species, as well as within the same species, is explained not by the variety of discrete units of a lower order (cells, tissues, organs), but by the complexity of their combinations, which provide qualitative characteristics of organisms. Currently, more than a million species of animals and about half a million plant species live on Earth. Each species consists of individual individuals (organisms, individuals) having their own distinctive features.
6. Population and species level. The totality of organisms of one species inhabiting a certain territory makes up a population. A population is an unorganized living system that is an elementary unit of the evolutionary process; speciation processes begin in it. The population is part of biocenoses.
7. Biocenotic level. Biogeocenoses are historically established stable communities of populations of various species, interconnected with the environment by metabolism, energy and information. They are elementary systems in which the material-energy cycle is carried out, due to the vital activity of organisms.
8. Biosphere level. The totality of biogeocenoses is: the biosphere and determine all the processes taking place in it.
Thus, we see that the question of structural levels in biology has some features in comparison with its consideration in physics. This feature is that the study of each level of organization in biology sets as its main goal the explanation of the phenomenon of life. Indeed, if in physics the division into structural levels of matter is rather arbitrary (the criteria here are mass and dimensions), then the levels of matter in biology differ not so much in dimensions or levels of complexity, but mainly in the laws of functioning.