Single-celled organisms were first discovered by the human eye in the 1670s, thanks to the Dutch naturalist, endowed with a great passion for understanding the world, Antonie van Leeuwenhoek. It was he who first examined these “little animals” with the help of his incredible lenses. Their scientific study began later - and has not stopped to this day. Single-celled organisms live everywhere, including in conditions where other organisms cannot survive.
What distinctive features inherent in unicellular organisms?
1. Morphologically, unicellular organisms are a single cell. However, in terms of its functions it is self-sufficient organism, which can move in space, reproduce, and feed. The sizes of single-celled organisms vary from a few microns to several centimeters. Several years ago, multinucleate xenophyophores with a diameter of at least 10 centimeters were discovered in the Mariana Trench.
2. Liquid medium- a fundamental condition for the existence of unicellular organisms. Moreover, this is not only the sea or a swamp, but also the liquids inside the body of a person or other creatures.
3. Single-celled organisms take over space and attract food closer using pseudopods(temporary, constantly changing shape outgrowths of ectoplasm, like an amoeba), flagella(thin, long organelles, threads of cytoplasm located in the front of the body, like in green euglena) and eyelashes(multiple outgrowths of cytoplasm throughout the body, like a ciliate). The flagella twist into the liquid like a corkscrew, and the cilia “flap”, creating a wave motion.
4. Most unicellular organisms - heterotrophs, that is, they eat ready-made organic substances. Euglena green - mixotroph, but the colonial Volvox - autotroph.
5. Irritability(the ability of a cell to change physical and chemical properties under the influence of environmental conditions), one of the basic properties of a living organism, manifests itself in protozoa taxis: reactions to any irritation. Single-celled organisms move either towards a stimulus (for example, a piece of food) or away from it.
6. Reflexes unicellular organisms do not have due to the lack of a nervous system.
8. During asexual reproduction of protozoa, unlike multicellular ones, there is no destruction nuclear envelope during cell division.
9. Of course, protozoa have mitochondria.
The meaning of single-celled animals
1. Protozoa are eaten by larger invertebrates.
2. Over hundreds of thousands of years, the external and internal skeletons of testate amoebae, foraminifera, radiolarians and other similar creatures formed marine sedimentary rocks that humans use in construction (for example, shell rock).
Class Flagellates
Structure. Flagellates have flagella that serve as organelles of movement and facilitate the capture of food. There may be one, two or many. The movement of the flagellum in surrounding water a whirlpool is caused, due to which small particles suspended in water are carried 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 developed cytoskeletal elements, determines the constant shape of the body.
Genetic apparatus
in most flagellates it is represented by a single nucleus, but there are also binucleate (for example, Giardia) and multinucleate (for example, opalina) species.
Cytoplasm
It is clearly divided into a thin outer layer - transparent ectoplasm and deeper endoplasm.
Method of nutrition. 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 solar radiation energy. Chlorophyll is found in chromatophores, similar in organization to plant plastids. Many flagellates with a plant type of nutrition have special devices that perceive light stimulation - stigmas.
Heterotrophic organisms (trypanosome - the causative agent of sleeping sickness) do not have chlorophyll and therefore cannot synthesize carbohydrates from inorganic substances. Mixotrophic organisms are capable of photosynthesis, but also feed on minerals and organic substances created by other organisms (green euglena).
Osmoregulatory
and partly the excretory functions are performed in flagellates, like in sarcodidae, by contractile vacuoles, which are present in free-living freshwater forms.
Reproduction. In flagellates, sexual and asexual reproduction is observed. The usual form of asexual reproduction is longitudinal fission.
Habitat. Flagellates are widespread in fresh water bodies, especially small ones and polluted with organic residues, as well as in the seas. Many species parasitize various animals and humans and thereby cause great harm (tryponosomes, intestinal parasites, etc.).
This reference book contains all the theoretical material on the biology course necessary for passing the Unified State Exam. It includes all elements of content, verified by test materials, and helps to generalize and systematize knowledge and skills for a secondary (high) school course.
Theoretical material is presented in a concise, accessible form. Each section is accompanied by examples test tasks, allowing you to test your knowledge and degree of preparedness for the certification exam. Practical tasks correspond to the Unified State Exam format. At the end of the manual, answers to tests are provided that will help schoolchildren and applicants test themselves and fill in existing gaps.
The manual is addressed to schoolchildren, applicants and teachers.
Reproduction of ciliates occurs both asexually and sexually. During asexual reproduction, longitudinal cell division occurs. During the sexual process, a cytoplasmic bridge is formed between two ciliates. Polyploid (large) nuclei are destroyed, and diploid (small) nuclei are divided by meiosis to form four haploid nuclei, three of which die, and the fourth is divided in half, but by mitosis. Two nuclei are formed. One is stationary and the other is migratory. Then, an exchange of migrating nuclei occurs between the ciliates. Then the stationary and migrated nuclei merge, the individuals disperse and large and small nuclei are formed in them again.
A1. The taxon into which all protozoa are grouped is called
1) kingdom
2) sub-kingdom
A2. Protozoa do not
2) organelles 4) sexual reproduction
A3. With the complete oxidation of 1 molecule of glucose, the amoeba produces ATP in the amount
1) 18 g/mol 3) 9 g/mol
2) 2 g/mol 4) 38 g/mol
1) amoeba proteus 3) trypanosoma
2) green euglena 4) radiolaria
A5. Through the contractile vacuole in ciliates occurs
1) removal of solid waste products
2) release of liquid waste products
3) excretion of germ cells - gametes
4) gas exchange
1) mosquito blood 3) mosquito larvae
2) mosquito saliva 5) mosquito eggs
A7. Asexual reproduction malarial plasmodium occurs in
1) human erythrocytes
2) red blood cells and mosquito stomach
3) human leukocytes
4) human erythrocytes and liver cells
A8. Which organelle is missing in ciliate cells?
1) nucleus 3) mitochondria
2) chloroplasts 4) Golgi apparatus
A9. What do Euglena and Chlorella have in common?
1) the presence of glycogen in cells
2) ability to photosynthesize
3) anaerobic respiration
4) presence of flagella
A10. Not found among ciliates
1) heterotrophic organisms
2) aerobic organisms
3) autotrophic organisms
A11. The most complex
common amoeba 3) malarial plasmodium
Euglena green 4) ciliate-slipper
A12. During cold weather and other unfavorable conditions, free-living protozoa
1) form colonies 3) form spores
2) actively move 4) form cysts
Part B
B1. Select the protozoa leading a free lifestyle
1) ciliate stentor 4) lamblia
2) amoeba proteus 5) stylonychia
3) trypanosoma 6) balantidium
B2. Match the representative of the protozoa with the trait it has
Unicellular or Protozoa. General characteristics" class="img-responsive img-thumbnail">
Part WITH
C1. Why do aquarists grow ciliate culture in milk?
C2. Find errors in the given text, correct them, indicate the numbers of the sentences in which they are made. 1. Protozoa (single-celled) organisms live only in fresh waters. 2. A protozoan cell is an independent organism, with all the functions of a living system. 3. Unlike the cells of multicellular organisms, the cells of all protozoa have the same shape. 4. Protozoa feed on solid food particles and bacteria. 5. Undigested food remains are removed through contractile vacuoles. 6. Some protozoa have chromatophores containing chlorophyll and are capable of photosynthesis.
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Basic terms and concepts tested in exam paper: amoebas, balantidium, flagellates, ciliates, coccidia, malarial plasmodium, digestive vacuole, sexual progress, powder, sarcodaceae, contractile vacuole, sporozoans, green euglena.
The body of the simplest animals consists of one cell that performs all vital functions. Representatives of this subkingdom have all the properties of an independent organism. Free-living protozoa have additional organelles for movement, nutrition, excretion, protection, etc. Some of these organelles are temporary (amoeba pseudopods), some are permanent (euglena flagellum, ciliate cilia).
The role of protozoa in nature and human life:
– are indispensable participants in the circulation of substances and energy in ecosystems, acting as micro-consumers and decomposers;
– form geological deposits of limestone and chalk;
– are objects scientific research;
Class Flagellates. Representatives of this class have a constant body shape due to the presence of a compacted cell membrane.
Euglena green has a spindle-shaped body. The cell size is about 0.05 mm. Euglena moves with the help of a flagellum - a cytoplasmic outgrowth consisting of thin fibrils. At the front end there is a light-sensitive peephole. In the cytoplasm, in addition to all the organelles characteristic of animal cells, there are chromatophores containing chlorophyll. In the light, euglena is capable of photosynthesis. Therefore, it is classified as an intermediate evolutionary form between plants and animals. Euglena reproduces asexually, by dividing in two along the longitudinal axis. Sexual reproduction occurs through copulation(cell fusion).
Volvox is one of the colonial forms of flagellates.
Type of ciliates. Class ciliated ciliates. The phylum has about 6 thousand species.
Representatives: slipper ciliates, trumpeter ciliates.
The slipper ciliate is an animal measuring 0.1-0.3 mm.
Its cell membrane is covered with cilia, which are used for movement. There are two nuclei in a cell - vegetative , polyploid And generative , diploid. The oral cavity on the body forms an oral funnel, which turns into a cellular mouth leading to throat. Form in the pharynx digestive vacuoles digesting food. Undigested food remains are removed through the hole - powder .
The slipper ciliate has two contractile vacuoles located at opposite ends of the body. Excess water and metabolic products are removed through them.
Reproduction of ciliates occurs both asexually and sexually. During asexual reproduction, longitudinal cell division occurs. During the sexual process, a cytoplasmic bridge is formed between two ciliates. Polyploid (large) nuclei are destroyed, and diploid (small) nuclei are divided by meiosis to form four haploid nuclei, three of which die, and the fourth is divided in half, but by mitosis. Two nuclei are formed. One is stationary and the other is migratory. Then, an exchange of migrating nuclei occurs between the ciliates. Then the stationary and migrated nuclei merge, the individuals disperse and large and small nuclei are formed in them again.
Definition 1
Unicellular (protozoa) are organisms in which all the functions of living things are performed by one cell.
In addition to prokaryotes, these include unicellular eukaryotes, among which there are plants, animals, and fungi.
Features of single-celled organisms
The sizes of protozoa are microscopically small. The peculiarities of unicellular organisms include the fact that they perform all the functions of living things with the help of cellular organelles and are a separate independent organism, represented by only one cell. In structure and set of organelles, the cells of unicellular organisms are similar to the cells of multicellular organisms. Among unicellular eukaryotes, there are both simply constructed organisms (amoeba, chlorella) and quite complex ones (ciliates, acetabularia).
If the cells of multicellular organisms are characterized by differentiation of functions and the inability to perform all the functions of a living thing at once, then unicellular organisms retain this ability. High level their organization is cellular. The cell of unicellular organisms is an integral organism that has all the properties of a living thing: metabolism, irritability, growth, reproduction, and the like.
Their body consists of cytoplasm, in which there are outer layer- ectoplasm, and internal - endoplasm. In most species, the outside of the cell is covered with a membrane, which provides the single-celled animal with a permanent shape. Protozoa exhibit organelles that perform various functions:
- digestion (digestive vacuoles),
- secretions (contractile vacuoles),
- movements (flagella, cilia),
- perception of light (photosensitive eye)
and other organelles that provide all vital processes. According to the method of nutrition, these are heterotrophic organisms. Protozoa are characterized by irritability, which manifests itself in various movements - taxis. There are positive taxis - movements towards the stimulus, and negative taxis - movements away from the stimulus.
When exposed to unfavorable conditions, protozoa form cysts. Encystment is important biological feature protozoa. It not only provides survival from unfavorable conditions, but also promotes widespread settlement.
Aquatic unicellular
Marine unicellular animals, such as foraminifera and radiolarians, have an external skeleton in the form of a calcareous shell. Highly organized unicellular animals include ciliates. The organelles of movement in them are cilia; the body is covered with a durable elastic shell, which gives it a constant shape. Most ciliates have two nuclei: large and small. Large vegetative nucleus - regulates the processes of movement, nutrition, excretion, as well as asexual reproduction, carried out by transverse division of the cell in half. The small nucleus is generative; it performs an important function in the sexual process.
Among aquatic unicellular organisms, mixotrophs are also distinguished - organisms that can feed both through photosynthesis and heterotrophy. For example, green euglena.
Euglena lives in freshwater bodies of water and swims using a single flagellum located at the front end of the body. In the cytoplasm of euglena there are chloroplasts containing chlorophyll, which allows euglena to feed phototrophically. If there is no light, it switches to heterotrophic nutrition. Thanks to this property, euglena combines the characteristics of a plant and an animal, which indicates the evolutionary unity of the plant and animal world.
Unicellular plants and fungi
Note 1
In nature there are many not only single-celled animals, but also single-celled plants and fungi. For example, among green algae, Chlamydomonas and Chlorella are unicellular representatives, and among fungi, yeast is unicellular.
Single-celled plants and animals are typical eukaryotic cells that have the corresponding organelles:
- surface membrane,
- core,
- mitochondria,
- Golgi apparatus,
- endoplasmic reticulum,
- ribosomes.
Differences in the structure of unicellular animals and unicellular plants are associated with differences in the way they feed. For plant cells characterized by the presence of plastids, vacuoles, cell walls and other features associated with photosynthesis. Animal cells are characterized by the presence of a glycocalyx, digestive vacuoles and other features associated with heterotrophic nutrition.
In fungi, the cell has a cell wall, which shows the similarity of fungi with bacteria and plants. But mushrooms are heterotrophs, and this makes them similar to animals.
Single-celled eukaryotes reproduce predominantly asexually, but in some of them (for example, the slipper ciliates) a sexual process is observed - the exchange of genetic information, and in others (for example, chlamydomonas) sexual reproduction occurs. Asexual reproduction occurs by cell division in half through mitosis. During sexual reproduction, gametes are produced, which then fuse to form a zygote.
Note 2
