Features of the structure of unicellular organisms. Protozoa

There are about 70,000 species of single-celled animals in the world's fauna.

Almost all simple ones have microscopic sizes (from 2 microns to 0.2 mm), among them there are also colonial forms (Volvox). Single-celled organisms live in freshwater (common amoeba, green euglena, slipper ciliates, volvox) and marine reservoirs (foraminifera, promenacia), in soil (some types of amoebas, flagellates, ciliates).

The simplest are representatives of the animal world, located at the cellular level of organization. Morphologically they constitute one cell, but functionally they constitute an entire organism. Therefore, a protozoan cell is built much more complex than a cell of a multicellular organism.

This is explained by the fact that the cells of multicellular organisms perform only certain functions, while one cell of a protozoan performs all the vital functions inherent in a whole organism: nutrition, movement, excretion, respiration, reproduction, etc.

Features of the structure and life activity of unicellular organisms (protozoa)

The protozoan cell, like any eukaryotic cell, has general cellular organelles. In the cytoplasm of protozoa there are two layers: the outer - ectoplasm and the inner - endoplasm. In addition, protozoa have organelles characteristic only of them: movement (psepododes, flagella, cilia), digestion (digestive vacuoles, in ciliates - cellular mouth, pharynx), excretion and osmoregulation (contractile vacuoles).

The cell of unicellular animals contains one (amoeba, euglena) or several (ciliates) nuclei. The vast majority of single-celled organisms have the ability to move. With the help of temporary protrusions of the cytoplasm - false legs (pseudopods), simple ones, lacking a dense cell membrane (amoebas), move. The rapid movement of single-celled organisms is facilitated by flagella (green euglena) and cilia (slipper ciliates).

The feeding methods of protozoa are varied. Most of them feed heterotrophically. In amoebas, food enters the cytoplasm with the help of pseudopodia that 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 remains are removed from the cell in any place to which the digestive vacuole (amoeba) approaches or through special openings (powder in the ciliate slipper).

Among unicellular animals there are species that feed like green plants (Volvox). Their cytoplasm contains chromatophores - organelles with photosynthetic pigments. Some flagellates that have chromatophores (green euglena) have 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 flow of oxygen through the entire surface of the cell. It oxidizes complex organic substances to CO 2, H 2 O and other compounds. This releases energy, which is used for the vital processes of animals.

Protozoa are characterized by non-sexual and sexual methods of reproduction. Asexual reproduction occurs through division and budding. Single-celled organisms more often reproduce by dividing the mother organism into two daughter cells.

For the slipper ciliates, in addition to division, there is a characteristic sexual process, during which two ciliates temporarily connect with each other and exchange small nuclei. In this way, ciliates exchange genetic (hereditary) information contained in their nuclei.

Single-celled organisms are characterized by irritability—the body’s response to external influences. Single-celled organisms tolerate unfavorable environmental conditions in the state of a cyst - the cell is rounded, compressed, draws in organelles of movement and becomes covered with a thick membrane.

Soil formation processes are also carried out with the help of protozoa. Flagellated unicellular organisms are used for biological assessment of the degree of cleanliness of water bodies (biodiagnostics). Foraminifera and promenacia play a significant role in the formation of chalk and limestone deposits, which are valuable building materials.

Basic terms and concepts tested in the examination paper: amoebas, balantidium, flagellates, ciliates, coccidia, malarial plasmodium, digestive vacuole, sexual progress, powder, sarcodae, contractile vacuole, sporozoa, 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 of 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.

This reference book contains all the theoretical material on the biology course required to pass 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 of test tasks that allow 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) trypanosome

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 of falciparum 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 absent 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

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">

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.

The general features of the organization of protozoa are the following:

Most protozoa are unicellular, less often colonial organisms. Their unicellular body has the functions of an entire organism, which are performed by general-purpose organelles (nucleus, endoplasmic reticulum, Golgi complex, lysosomes, mitochondria, ribosomes, etc.) and special ones (digestive and contractile vacuoles, flagella, cilia, etc.). Working in harmony, they obesprovide a single cell with the possibility of existing inas an independent organism.

The integuments of protozoa are represented either only plasmatichemical membrane, or also a dense, fairly flexible and elastic shell - pellicle, giving them relative constancy of body shape. In the cytoplasm, two layers are clearly distinguished: superficial, denser - ectoplasma, and internal, more liquid and granular - endoplasma, in which the organelles of the protozoa are located. Due to the colloidal properties of the cytoplasm, these two layers can mutually transform into each other.

Organelles of movement of most species - pseudopods, flagella or numerous short cilia.

Gas exchange occurs over the entire surface of the body.

Irritability in protozoa manifests itself in the form taxis.

9. Most protozoa have the ability to tolerate unfavorable conditions in a dormant stage cysts. In this case, the cell becomes rounded, retracts or discards movement organelles, and becomes covered with a dense protective membrane. The cyst stage allows the protozoan not only to survive unfavorable conditions in an inactive state, but also to spread. Once in favorable conditions, the protozoan leaves the cyst shell and begins to feed and reproduce.

To the sub-kingdom Protozoa are unicellular animals. Some species form colonies.

A protozoan cell has the same structure as a cell of a multicellular animal: it is limited by a membrane, the internal space is filled with cytoplasm, which contains the nucleus (nuclei), organelles and inclusions.

The cell membrane in some species is represented by the outer (cytoplasmic) membrane, in others - by the membrane and pellicle. Some groups of protozoa form shells around themselves. The membrane has a structure typical of a eukaryotic cell: it consists of two layers of phospholipids, into which proteins are “immersed” to different depths.

Number of cores - one, two or more. The shape of the kernel is usually round. The core is bounded by two membranes, these membranes are permeated with pores. The internal contents of the nucleus are nuclear juice (karyoplasm), which contains chromatin and nucleoli. Chromatin consists of DNA and proteins and is an interphase form of chromosome existence (decondensed chromosomes). The nucleolus is composed of rRNA and proteins and is the site where ribosomal subunits are formed.

The outer layer of the cytoplasm is usually lighter and denser - ectoplasm, the inner layer - endoplasm.

The cytoplasm contains organelles characteristic of both the 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 (breakdown of organic substances), ribosomes (protein synthesis), cell center with centrioles (formation of microtubules, in particular spindle microtubules), microtubules and microfilaments (cytoskeleton). Organelles of protozoa, characteristic only of this group of animals: stigmas (light perception), trichocysts (defense), axtostyle (support), contractile vacuoles (osmoregulation), etc. Organelles of photosynthesis, present in plant flagellates, are called chromatophores. The organelles of protozoan movement are represented by pseudopodia, cilia, and flagella.

Nutrition - heterotrophic; in plant flagellates - autotrophic, can 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.

When unfavorable conditions occur, most protozoa form cysts. Encystment is a way of surviving unfavorable conditions.

The main method of reproduction of protozoa 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. Asexual reproduction is based on mitosis. In a number of species, the sexual process takes place - conjugation (ciliates) and sexual reproduction (sporophytes).

Habitats: marine and fresh water bodies, soil, plant, animal and human organisms.

Classification of protozoa

• Subkingdom Protozoa, or Single Cells (Protozoa)
  • Type Sarcomastigophora
    • Subphylum Flagellates (Mastigophora)
      • Class Plant flagellates (Phytomastigophorea)
      • Class Animal flagellates (Zoomastigophorea)
    • Subtype Opalina (Opalinata)
    • Subtype Sarcodina
      • Class Rhizopoda (Rhizopoda)
      • Class Radiolaria, or Rays (Radiolaria)
      • Class Sunflowers (Heliozoa)
  • Type Apicomplexa
    • • Perkinsea class
      • Class Sporozoea
  • Phylum Myxosporidium (Myxozoa)
    • • Class Myxosporea
      • Class Actinosporidia (Actinosporea)
  • Type Microsporidia (Microspora)
  • Type of Ciliates (Ciliophora)
    • • Class Ciliated ciliates (Ciliata)
      • Class Sucking ciliates (Suctoria)
  • Type Labyrinthula (Labirinthomorpha)
  • Type Ascetosporidia

Protozoa appeared about 1.5 billion years ago.

Protozoa belong to primitive unicellular eukaryotes (superkingdom Eucariota). It is now generally accepted that eukaryotes evolved from prokaryotes. There are two hypotheses for the origin of eukaryotes from prokaryotes: a) successive, b) symbiotic. According to the successive hypothesis, membrane organelles arise gradually from the plasmalemma of prokaryotes. According to the symbiotic hypothesis (endosymbiotic hypothesis, symbiogenesis hypothesis), a eukaryotic cell arises as a result of a series of symbioses of several ancient prokaryotic cells.