Features of unicellular organisms. The value of unicellular
Class Flagella
Structure. Flagellates have flagella that serve as organelles of movement and contribute to the capture of food. There may be one, two or many. The movement of the flagellum in the surrounding water causes a whirlpool, due to which small particles suspended in water are carried away to the base of the flagellum, where there is a small opening - a cellular mouth leading to a deep canal-pharynx.
Almost all flagellates are covered with a dense elastic membrane, which, along with the developed elements of the cytoskeleton, determines the permanent shape of the body.
genetic apparatus
in most flagellates it is represented by a single nucleus, but there are also binuclear (for example, Giardia) and multinuclear (for example, opal) species.
Cytoplasm
it is clearly divided into a thin outer layer - a transparent ectoplasm and a deeper lying endoplasm.
Nutrition method. According to the method of feeding, flagellates are divided into three groups. Autotrophic organisms, as an exception in the animal kingdom, synthesize organic substances (carbohydrates) from carbon dioxide and water with the help of chlorophyll and the energy of solar radiation. Chlorophyll is found in chromatophores similar in organization to plant plastids. Many flagellates with a vegetable type of nutrition have special apparatuses that perceive light stimuli - stigmas.
Heterotrophic organisms (trypanosoma - the causative agent of sleeping sickness) do not have chlorophyll and therefore cannot synthesize carbohydrates from not organic matter. Mixotrophic organisms are capable of photosynthesis, but also feed on mineral and organic substances created by other organisms (green euglena).
Osmoregulatory
and partly the excretory functions are performed in flagellates, as in sarcodes, by contractile vacuoles, which are present in free-living freshwater forms.
Reproduction. Flagellates have sexual and asexual reproduction. The usual form of asexual reproduction is longitudinal fission.
Habitat. Flagellates are widely distributed in fresh water bodies, especially small and polluted with organic residues, as well as in the seas. Many species parasitize various animals and humans and thus cause great harm (tryponosomes, intestinal parasites, etc.).
Type of protozoa
Sarcomastigophores
Sarcode
Proteus amoeba (common), dysenteric amoeba, radiolaria
Flagella
Euglena green, Volvox, African trypanosoma, Leishmania, Trichomonas, Giardia hepatic
spores
coccidiae
Malarial Plasmodium
ciliates
Eyelash
Infusoria-balantidia, infusoria-shoe, infusoria-trumpeter
Trichofriosis
Used Books:
1.Biology: complete reference to prepare for the exam. / G.I. Lerner. - M.: AST: Astrel; Vladimir; VKT, 2009 2. Biology: Animals: textbook. for 7-8 cells. general education institutions. - 7th ed. - M.: Education, 2000. 3. Biology: study guide / A.G. Lebedev. M.: AST: Astrel. 2009. 4. Biology. Full course general education high school: tutorial for schoolchildren and entrants / M.A.Valovaya, N.A.Sokolova, A.A. Kamensky. - M.: Exam, 2002. 5. Biology for university applicants. Intensive course/ G.L. Bilich, V.A. Kryzhanovsky. - M.: Onyx Publishing House, 2006.
Used Internet resources:
There are about 70,000 species of unicellular animals in the world fauna.
Almost all simple ones are microscopic in size (from 2 microns to 0.2 mm), among them there are also colonial forms (volvox). Single-celled organisms live in fresh water (common amoeba, green euglena, ciliate shoe, volvox) and marine water bodies (foraminifera, promenades), in the soil (some types of amoeba, flagellates, ciliates).
The simplest are representatives of the animal world, located at the cellular level of organization. Morphologically, they constitute one cell, and functionally they constitute an integral organism. Therefore, the cell of the simplest is built much more complicated than the cell of a multicellular organism.
This is due to the fact that the cells of multicellular organisms perform only certain functions, while one cell of the simplest performs all the vital functions inherent in the whole organism: nutrition, movement, excretion, respiration, reproduction, etc.
Features of the structure and vital activity of unicellular organisms (protozoa)
The protozoan cell, like any eukaryotic cell, has general cellular organelles. In the cytoplasm of protozoa, two layers are distinguished: the outer - ectoplasm and the inner - endoplasm. In addition, the protozoa have organelles characteristic only of them: movements (pseudopodia, flagella, cilia), digestion (digestive vacuoles, ciliates have a cellular mouth, pharynx), excretion and osmoregulation (contractile vacuoles).
A cell of unicellular animals contains one (ameba, euglena) or several (ciliates) nuclei. The vast majority of unicellular organisms have the ability to move. With the help of temporary bulges of the cytoplasm - false legs (pseudo-legs), simple ones, devoid of a dense cell membrane (ameba), move. Flagella (euglena green) and cilia (ciliates-shoe) contribute to the rapid movement of unicellular organisms.
The ways of feeding protozoa are varied. Most of them feed heterotrophically. In amoeba, food enters the cytoplasm with the help of pseudopodia, which capture it. In ciliates, vibrations of the cilia cause food to enter the cellular mouth and pharynx.
Digestion of food occurs in digestive vacuoles. Undigested food residues are removed from the cell in any place to which the digestive vacuole (amoeba) approaches or through special openings (powder in ciliates-shoes).
Among unicellular animals, there are species that feed like green plants (volvox). In their cytoplasm there are chromatophores - organelles with photosynthetic pigments. For some flagellates with chromatophores (euglena green), a characteristic mixed (mixotrophic) type of nutrition. In the light, they are capable of photosynthesis, and in the dark they feed on ready-made organic substances.
Respiration is carried out by the supply of oxygen through the entire surface of the cell. It oxidizes complex organic substances to CO 2 , H 2 O and other compounds. At the same time, energy is released, which is used for the life processes of animals.
For protozoa, asexual and sexual methods of reproduction are characteristic. Asexual reproduction is carried out by division and budding. More often single-celled ones reproduce by dividing the mother's organism into two daughter cells.
For ciliates-shoes, in addition to the section, there is a characteristic sexual process, during which two ciliates are temporarily connected to each other and exchange small nuclei. Thus ciliates exchange genetic (hereditary) information contained in their nuclei.
Unicellular is characterized by irritability - the response-reaction of the body to external influences. Unfavourable conditions external environment unicellular are transferred in the state of a cyst - the cell is rounded, compressed, draws in the organelles of movement and is covered with a thick membrane.
Soil formation processes are also carried out with the help of protozoa. Flagellar unicellular serve for the biological assessment of the degree of purity of water bodies (biodiagnostics). Foraminifers and promenacs play a significant role in the formation of chalk and limestone deposits, which are valuable building materials.
To the sub-kingdom Protozoa are unicellular animals. Some species form colonies.
The protozoan cell has the same structural scheme as the cell of a multicellular animal: it is limited by a membrane, the inner space is filled with cytoplasm, in which the nucleus (nuclei), organelles and inclusions are located.
The cell membrane in some species is represented by an outer (cytoplasmic) membrane, in others - by a membrane and a pellicle. Some groups of protozoa form a shell around themselves. The membrane has a structure typical of a eukaryotic cell: it consists of two layers of phospholipids, into which proteins “sink” to different depths.
The number of cores is one, two or more. The shape of the nucleus is usually rounded. The nucleus is bounded by two membranes, these membranes are permeated with pores. The internal content of the nucleus is the nuclear juice (karyoplasm), which contains chromatin and nucleoli. Chromatin consists of DNA and proteins and is an interphase form of the existence of chromosomes (decondensed chromosomes). The nucleolus is composed of rRNA and proteins and is the site where ribosome subunits are formed.
The outer layer of the cytoplasm is usually lighter and denser - ectoplasm, the inner - endoplasm.
In the cytoplasm there are organelles characteristic of both cells of multicellular animals, and organelles characteristic only of this group of animals. Organelles of protozoa, common with organelles of a multicellular animal cell: mitochondria (ATP synthesis, oxidation of organic substances), endoplasmic reticulum (transport of substances, synthesis of various organic substances, compartmentalization), Golgi complex (accumulation, modification, secretion of various organic substances, synthesis of carbohydrates and lipids , the site of formation of primary lysosomes), lysosomes (cleavage of organic substances), ribosomes (protein synthesis), cell center with centrioles (formation of microtubules, in particular, spindle microtubules), microtubules and microfilaments (cytoskeleton). Protozoan organelles, characteristic only for this group of animals: stigmas (light perception), trichocysts (protection), axtostyle (support), contractile vacuoles (osmoregulation), etc. Photosynthesis organelles found in plant flagellates are called chromatophores. The organelles of protozoan movement are represented by pseudopodia, cilia, and flagella.
Nutrition - heterotrophic; in plant flagellates - autotrophic, may be mixotrophic.
Gas exchange occurs through the cell membrane, the vast majority of protozoa are aerobic organisms.
The response to environmental influences (irritability) manifests itself in the form of taxis.
On the onset adverse conditions most protozoa form cysts. Encystation is a way of experiencing adverse conditions.
The main method of protozoan reproduction is asexual reproduction: a) division of the mother cell into two daughter cells, b) division of the mother cell into many daughter cells (schizogony), c) budding. Mitosis is the basis of asexual reproduction. In a number of species, the sexual process takes place - conjugation (ciliates) and sexual reproduction (sporozoans).
Habitats: marine and fresh waters, soil, plant, animal and human organisms.
Classification of protozoa
- Subkingdom Protozoa, or Unicellular (Protozoa)
- Type Sarcomastigophora (Sarcomastigophora)
- Subtype Flagellates (Mastigophora)
- Class Plant flagellates (Phytomastigophorea)
- Class Animal flagellates (Zoomastigophorea)
- Opalina subtype (Opalinata)
- Subtype Sarcodaceae (Sarcodina)
- Rhizopeda class (Rhizopoda)
- Class Radiolaria, or Beams (Radiolaria)
- Class Sunflowers (Heliozoa)
- Subtype Flagellates (Mastigophora)
- Type Apicomplexa (Apicomplexa)
- Perkinsea class
- Class Sporozoa (Sporozoea)
- Type of Myxosporidium (Myxozoa)
- Class Myxosporea (Myxosporea)
- Class Actinosporidia (Actinosporea)
- Type of Microsporidia (Microspora)
- Type of ciliates (Ciliophora)
- Class Ciliary ciliates (Ciliata)
- Class Sucking ciliates (Suctoria)
- Type Labyrinthula (Labirinthomorpha)
- Ascetosporidia type (Ascetospora)
- Type Sarcomastigophora (Sarcomastigophora)
The simplest appeared about 1.5 billion years ago.
The simplest belong to the primitive unicellular eukaryotes (superkingdom Eucariota). It is now generally accepted that eukaryotes evolved from prokaryotes. There are two hypotheses of the origin of eukaryotes from prokaryotes: a) successive, b) symbiotic. According to the successive hypothesis, membranous organelles arise gradually from the plasmalemma of prokaryotes. According to the symbiotic hypothesis (endosymbiotic hypothesis, symbiogenesis hypothesis), eukaryotic cell arises as a result of a series of symbioses of several ancient prokaryotic cells.