According to modern cell theory, the mainThe structural and functional unit of living beings that live on the Earth is a cell. It is a complex open self-organizing and reproducing biosystem. The structure and functions of cells are studied by cytology and microbiology. The latter considers the specificity of the life of bacteria, which are prokaryotic organisms. In this article, we will study the types of cellular organization: mono- and multicellular organisms, colonial forms, as well as structural features of prokaryotic and eukaryotic cells.
In biology, there are 6 levels of organization of life:molecular, cellular, organismic, population-species, biogeocenotic and biospheric. Consider the cellular level of the organization, in which metabolic (metabolic and energy) reactions take place in the cells, and reproduction is also ensured. At the heart of this process is the transfer of hereditary traits (genes) from the parent to the daughter cells.
Thus, unicellular organisms are,in essence, absolutely integral and independent individuals, identical in form to functions having organs and tissues. More complex types of cellular organization are colonial and multicellular. On an example volvoksa we will consider features of colonial forms. It consists of cells of different types: vegetative and generative, although cytoplasm bound by outgrowths with each other, but functioning more autonomously. Colonies of green algae volvox - a clear example of the evolutionary development of living matter from unicellular to multicellular organisms, which have the most complex structure. Their cells combine into tissues, and form organs performing various functions.
The cellular level of organization in such organismsis transformed into specialized structures - the system (respiratory, digestive, excretory, etc.) Thus, the multicellular organism functions as an indivisible whole, and the cells are its structural units.
Cells, in which the core is absent, and the hereditary material - DNA molecules - are located directly in a denser cytoplasm layer, are called prokaryotic.
The types of cellular organization in which the basislies a sign of the presence or absence of a nucleus, these are prokaryotes and eukaryotes. As mentioned earlier, nuclear-free cells: bacteria and cyanobacteria, have a specific structure associated with the peculiarities of metabolism. Let us list them: this absence in the cell of such organelles as mitochondria, Golgi apparatus, lysosomes, vacuoles, cell center, endoplasmic reticulum. There are ribosomes that synthesize bacterial protein, there are rare gas vacuoles (idioadaptation to life in water bodies or in moist soil). Some forms contain organelles of motion - flagella.
Cytologists, continuing to study the types of cellularorganizations, found that nuclear cells have a very complex system of organelles, which ensures their metabolism and energy. Thanks to the coordinated work of organelles, their internal environment is characterized by a constant composition and properties - the so-called cellular homeostasis.
Eukaryotes, which include fungal cells,plants, animals and humans, contain the nucleus, endoplasmic reticulum, Golgi complex, mitochondria, ribosomes, cell center, lysosomes, plastids and vacuoles. In eukaryotes, the process of cell division is especially difficult. It is accompanied by the formation of an entire system, called the spindle of division.
Comparing prokaryotic and eukaryotic typescell organization, we find that they have both similarities and significant differences. For example, the process of oxidation of organic compounds by oxygen absorbed by cells of bacteria and nuclear organisms leads to similar results: the splitting of glucose to carbon dioxide and water, with the release of portions of energy in the form of synthesized ATP molecules.
This substance is a universal sourceenergy for both non-nuclear organisms and eukaryotes. Differences in cellular respiration are found by examining the structures that carry out this process. In nuclear organisms, it occurs on the crystals of mitochondria with the help of an enzymatic system - the Krebs cycle, and in bacteria it occurs on the folds of the cytoplasmic membrane on which the enzymes are located.
Microbiology studies bacteria and cyanobacteria,which are prokaryotic organisms. Bacteria differ in their form and have corresponding names: cocci (in the form of small single balls), vibrios (having the form of commas), staphylococci (resembling a bunch of grapes). Such cyanobacteria as nostok, anabena, are denuclearized cells with a mucosal cell wall, they differ from bacteria in that they contain photosynthesizing pigments found in chromatophores.
All the above examples show that the cellular organization of various microorganisms is diverse and conditioned by the peculiarities of their structure and vital activity.
