According to modern cellular theory, the main structural and functional unit of living creatures living on Earth is the 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 specifics of the life of bacteria that are prokaryotic organisms. In this article, we will study the types of cell organization: unicellular and multicellular organisms, colonial forms, as well as structural features of prokaryotic and eukaryotic cells.
Levels of organization of living matter
In biology, there are 6 levels of life organization: molecular, cellular, organismic, population-specific, biogeocenotic, and biospheric. Consider the cellular level of organization at which metabolic (metabolic and energy) reactions take place in cells, and reproduction is also ensured. The basis of this process is the transfer of hereditary traits (genes) from parent to daughter cells.
Thus, unicellular organisms are essentially completely integral and independent individuals, identical in function to forms that have organs and tissues. More complex types of cell organization are colonialism and multicellularity. Using Volvox as an example, consider the features of colonial forms. It consists of different types of cells: vegetative and generative, although they are connected by cytoplasm outgrowths with each other, but they function more autonomously. Colonies of volvox green algae are a good 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 that perform various functions.
The cellular level of organization in such organisms is transformed into specialized structures - systems (respiratory, digestive, excretory, etc.). Thus, a multicellular organism functions as an indivisible whole, and the cells are its structural units.
Features of prokaryotic organisms
Cells in which there is no nucleus, and hereditary material - DNA molecules - are located directly in a denser layer of the cytoplasm, called prokaryotic.
The types of cell organization that are based on a sign of the presence or absence of a nucleus are prokaryotes and eukaryotes. As already mentioned, nuclear-free cells: bacteria and cyanobacteria, have a specific structure associated with the characteristics of metabolism. We list them: this is the absence in the cell of such organelles as mitochondria, the Golgi apparatus, lysosomes, vacuoles, the cell center, and the endoplasmic reticulum. There are ribosomes synthesizing a bacterial protein, gas vacuoles are rarely found (idioadaptation to life in water bodies or in moist soil). Some forms contain organelles of movement - flagella.
Complication of the structure and functions of eukaryotes
Cytologists, while continuing to study the types of cellular organization, found that nuclear cells have a very complex system of organelles, providing 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 cells of fungi, 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 particularly difficult. It is accompanied by the formation of a whole system called the spindle of division.
Differences in metabolism in prokaryotes and eukaryotes
Comparing the prokaryotic and eukaryotic types of cell organization, we find that they have both similarities and quite serious differences. For example, the oxidation of organic compounds by oxygen absorbed by the cells of bacteria and nuclear organisms leads to similar results: the breakdown 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 source of energy for both nuclear-free organisms and eukaryotes. The differences in cellular respiration can be found by considering the structures that this process implements. In nuclear organisms, it occurs on mitochondrial cristae using an enzymatic system, the Krebs cycle, and in bacteria, it occurs on the folds of the cytoplasmic membrane on which enzymes are located.
Types of cellular organization of microorganisms
Microbiology studies bacteria and cyanobacteria, which are prokaryotic organisms. Bacteria are distinguished by their shape and have corresponding names: cocci (in the form of small single balls), vibrios (in the form of commas), staphylococci (resembling a bunch of grapes). Such cyanobacteria, such as nostock, anabena, are nuclear-free cells having a mucous cell wall; they differ from bacteria in that they contain photosynthetic pigments located in chromatophores.
All of the above examples indicate that the cellular organization of various microorganisms is diverse and is due to the peculiarities of their structure and activity.