Protozoa are extremely diverse in their structure. The smallest ones are 2-4 microns in diameter (a micrometer is 0.001 mm). Their most common sizes are in the range of 50-150 microns, some reach 1.5 mm and are visible to the naked eye.

The amoeba has the simplest structure. The body of the amoeba is a lump of semi-liquid cytoplasm with a nucleus in the middle. The entire cytoplasm is divided into two layers: the outer, viscous - ectoplasm and the inner, much more liquid - endoplasm. These two layers are not sharply demarcated and can transform into each other. The amoeba does not have a hard shell, and it is capable of changing the shape of its body. When an amoeba crawls along the leaf of an aquatic plant, protrusions of cytoplasm form in the direction in which it moves. Gradually, the rest of the amoeba's cytoplasm flows into them. Such protrusions are called pseudopods or pseudopodia. With the help of pseudopodia, the amoeba not only moves, but also captures food. With pseudopodia it envelops a bacterium or microscopic algae; soon the prey ends up inside the amoeba's body, and a bubble forms around it - a digestive vacuole. Undigested food remains are thrown out after some time.

Amoeba proteus: 1 - core; 2 - digestive vacuoles; 3 - contractile vacuole; 4 - pseudopods; 5 - undigested food residues thrown out.

In the cytoplasm of the amoeba, a light vesicle is usually visible, which appears and disappears. This is a contractile vacuole. It collects excess water that accumulates in the body, as well as liquid waste products of the amoeba. The amoeba, like all other protozoa, breathes over the entire surface of the body.

Euglena green: 1 - flagellum; 2 - eyespot; 3 - contractile vacuole;

The most complex structure of the simplest ciliates. Unlike amoeba, their body is covered with a thin shell and has a more or less constant shape. Supporting fibers running in different directions also support and determine the shape of the body. However, the body of ciliates can quickly contract, change its shape, and then return to its original shape. Contraction is carried out using special fibers, similar in many ways to the muscles of multicellular animals.

Ciliate slipper: 1 - cilia; 2 - digestive vacuoles; 3 - large nucleus (macronucleus); (micronucleus); 5 - mouth opening and pharynx; 6 - undigested food residues thrown out; 7 - trichocysts; 8 - contractile vacuole.

Ciliates can move very quickly. Thus, a shoe covers a distance in a second that exceeds the length of its body by 10-15 times. At the same time, many cilia that cover the entire body of the ciliate make rapid rowing movements, up to 30 per second (at room temperature). In the ectoplasm of the shoe there are many trichocyst rods. When irritated, they are thrown out, turning into long threads, and hit the enemy attacking the ciliate. Instead of those ejected, new trichocysts are formed in the ectoplasm. On one side, approximately in the middle of the body, the shoe has a deep oral cavity leading into a small tube-shaped pharynx. Through the pharynx, food enters the endoplasm, where it is digested in the resulting digestive vacuole. In ciliates, unlike amoebas, undigested food remains are thrown out in a specific place in the body. Their contractile vacuole is more complex and consists of a central reservoir and conducting channels. Ciliates have two types of nuclei: large - macronucleus and small - micronucleus. Some ciliates may have several macro- and micronuclei. The macronucleus differs from the micronucleus in having a significantly larger number of chromosomes. Consequently, it contains a lot of deoxyribonucleic acid (DNA), which is part of the chromosomes.

Various types of ciliates: 1 - trumpeter ciliate; 2-5 - planktonic ciliates.

Protozoa are irritable and therefore are able to choose the most favorable environmental conditions for themselves, reacting to light, heat, various chemicals, electric current, magnetic field and other stimuli.

Under unfavorable conditions, for example, when a body of water dries out or freezes, the protozoa take on a spherical shape, lose cilia or flagella, form a hard shell on its surface and turn into a motionless cyst. Protozoan cysts survive both desiccation and sudden temperature changes. Cysts are easily transported by the wind, with grass, hay, etc., which contributes to the spread of the species. If the cyst finds itself in suitable conditions, its shell bursts or holes appear in it, and the organism begins an active existence.

Protozoa in a drop of pond water (under a microscope).

Rhizome class unites the simplest unicellular animals, whose body is devoid of a dense shell and therefore does not have a permanent shape. They are characterized by the formation of pseudopods, which are temporarily formed outgrowths of the cytoplasm that facilitate movement and capture of food.

Habitat, structure and movement of amoeba. Common amoeba found in sludge at the bottom of the ponds with contaminated water. It looks like a small (0.2-0.5 mm), barely visible to the naked eye, colorless gelatinous lump, constantly changing its shape (“amoeba” means “changeable”). The details of the amoeba's structure can only be seen under a microscope.

The body of the amoeba consists of semi-liquid cytoplasm with a small bubble-shaped enclosed inside it core. An amoeba consists of one cell, but this cell is a whole organism leading an independent existence.

Cytoplasm cells are in constant motion. If the current of cytoplasm rushes to one point on the surface of the amoeba, a protrusion appears in this place on its body. It enlarges, becomes an outgrowth of the body - a pseudopod, cytoplasm flows into it, and the amoeba moves in this way. Amoeba and other protozoa capable of forming pseudopods are classified as rhizomes. They received this name due to the external resemblance of their pseudopods to plant roots.

Life activity of Amoeba.

Nutrition. In an amoeba, several pseudopods can form at the same time, and then they surround food - bacteria, algae, and other protozoa. Digestive juice is secreted from the cytoplasm surrounding the prey. A bubble is formed - a digestive vacuole. Digestive juice dissolves some of the substances that make up food and digests them. As a result of digestion, nutrients are formed that leak from the vacuole into the cytoplasm and are used to build the body of the amoeba. Undissolved residues are thrown out anywhere in the amoeba’s body.

Amoeba Breath. The amoeba breathes oxygen dissolved in water, which penetrates its cytoplasm through the entire surface of the body. With the participation of oxygen, complex food substances in the cytoplasm are decomposed into simpler ones. This releases the energy necessary for the life of the body.

Release of harmful substances life activity and excess water. Harmful substances are removed from the amoeba's body through the surface of its body, as well as through a special vesicle - a contractile vacuole. The water surrounding the amoeba constantly penetrates the cytoplasm, diluting it. The excess of this water with harmful substances gradually fills the vacuole. From time to time the contents of the vacuole are thrown out. So, food, water, and oxygen enter the amoeba’s body from the environment. As a result of the life activity of the amoeba, they undergo changes. Digested food serves as material for building the body of the amoeba. Substances that are harmful to the amoeba are removed outside. Metabolism occurs. Not only amoeba, but all other living organisms cannot exist without metabolism both within their body and with the environment.

Amoeba Reproduction. The amoeba's nutrition leads to the growth of its body. The grown amoeba begins to reproduce. (? Probably due to exceeding a certain mass of her body.) Reproduction begins with a change in the nucleus. It stretches out, is divided by a transverse groove into two halves, which diverge in different directions - two new nuclei are formed. The body of the amoeba is divided into two parts by a constriction. Each of them contains one core. The cytoplasm between both parts is torn and two new amoebas are formed. The contractile vacuole remains in one of them, but appears anew in the other. So, the amoeba reproduces by dividing in two. During the day, division can be repeated several times.

Division (reproduction) of Amoeba.

Cyst. Amoeba feeds and reproduces throughout the summer. In autumn, when cold weather sets in, the amoeba stops feeding, its body becomes rounded, and a dense protective shell is formed on its surface - a cyst is formed. The same thing happens when the pond dries out where amoebas live. In the state of a cyst, the amoeba tolerates living conditions unfavorable for it. When favorable conditions occur, the amoeba leaves the cyst shell. She releases pseudopods, begins to feed and reproduce. Cysts carried by the wind contribute to the dispersal (spread) of amoebas.

Possible additional questions for self-study.

  • What makes Cytoplasm systematically flow from one part of the Amoeba to another, forcing it to move in a given direction?
  • How does the membrane of Amoeba's cytoplasm recognize nutrients, as a result of which the amoeba purposefully forms pseudopods and a digestive vacuole?

A basic level of

For each task, choose one correct answer from the four proposed.

A1. Almost all animals eat

  1. autotrophic
  2. heterotrophic
  3. during photosynthesis
  4. during chemosynthesis

A2. Representatives of the kingdom have a nervous system

  1. mushrooms
  2. bacteria
  3. plants
  4. animals

AZ. The body is made up of one cell

  1. lichens
  2. cap mushrooms
  3. protozoa

A4. The pseudopods of protozoan animals are

  1. plastids
  2. nuclear matter
  3. growth of cytoplasm
  4. nutrient supply

A5. The organelle for excreting undigested food debris in protozoa is

  1. cyst
  2. flagellum
  3. powder

A6. Reproduction of protozoa occurs mainly through

  1. phagocytosis
  2. pinocytosis
  3. cell division
  4. cyst formation

A7. There is no permanent body shape

  1. foraminifera
  2. ciliates-slippers
  3. euglena green
  4. amoeba vulgaris

A8. Only in the cells of the simplest animals that feed autotrophically, there is

  1. chlorophyll
  2. cytoplasm
  3. flagellum

A9. Two nuclei are found in animal cells

  1. ciliates
  2. euglena
  3. Volvox
  4. amoebas

- - - Answers - - -

A1-2; A2-4; A3-4; A4-3; A5-4; A6-3; A7-4; A8-1; A9-1.

Increased difficulty level

B1. Are the following statements true?

A. Many simple animals are part of plankton.
B. Phagocytosis of protozoa is associated with the formation of a contractile vacuole.

  1. Only A is correct
  2. Only B is correct
  3. Both judgments are correct
  4. Both judgments are wrong

B2. Are the following statements true?

A. Amoeba captures food with pseudopods.
B. Among the representatives of the simplest animals, there are multicellular organisms.

  1. Only A is correct
  2. Only B is correct
  3. Both judgments are correct
  4. Both judgments are wrong

BZ. Choose three true statements. Absent in animal cells

  1. cell wall
  2. chloroplast
  3. cytoplasm
  4. outer membrane
  5. large vacuole

B4. Establish a correspondence between the structural feature of the animal and its species.

Features of the structure

    A. Presence of cilia
    B. Photosensitive eye
    B. Pseudopedia
    G. Chloroplast
    D. Two cores

Kind of animal

  1. Amoeba
  2. Euglena
  3. Ciliate slipper

Write down the corresponding numbers in the table.

- - - Answers - - -

B1-1; B2-1; B3-126; B4-32123.

The common amoeba (kingdom Animals, subkingdom Protozoa) has another name - Proteus, and is a representative of the class Sarcodidae free-living. It has a primitive structure and organization, moves with the help of temporary growths of cytoplasm, often called pseudopods. Proteus consists of only one cell, but this cell is a complete independent organism.

Habitat

The structure of an ordinary amoeba

The common amoeba is an organism consisting of one cell leading an independent existence. The body of the amoeba is a semi-liquid lump, 0.2-0.7 mm in size. Large individuals can be seen not only through a microscope, but also with a regular magnifying glass. The entire surface of the body is covered with cytoplasm, which covers the nucleus pulposus. During movement, the cytoplasm constantly changes its shape. Stretching out in one direction or the other, the cell forms processes, thanks to which it moves and feeds. Can push off algae and other objects using pseudopods. So, in order to move, the amoeba extends the pseudopod in the desired direction and then flows into it. The movement speed is about 10 mm per hour.

Proteus does not have a skeleton, which allows it to take any shape and change it as needed. The respiration of the common amoeba is carried out over the entire surface of the body; there is no special organ responsible for the supply of oxygen. During movement and feeding, the amoeba captures a lot of water. Excess of this fluid is released using a contractile vacuole, which bursts, expelling water, and then forms again. The common amoeba has no special sensory organs. But she tries to hide from direct sunlight and is sensitive to mechanical irritants and some chemicals.

Nutrition

Proteus feeds on single-celled algae, rotting debris, bacteria and other small organisms, which it captures with its pseudopods and pulls into itself so that the food ends up inside the body. Here a special vacuole is immediately formed, into which digestive juice is released. Amoeba vulgaris can feed anywhere in the cell. Several pseudopods can simultaneously capture food, then digestion of food occurs in several parts of the amoeba at once. Nutrients enter the cytoplasm and are used to build the amoeba’s body. Particles of bacteria or algae are digested, and the remaining waste is immediately removed outside. The common amoeba is capable of throwing out unnecessary substances in any part of its body.

Reproduction

Reproduction of the common amoeba occurs by dividing one organism into two. When the cell has grown sufficiently, a second nucleus is formed. This serves as a signal for division. The amoeba stretches out, and the nuclei disperse on opposite sides. A constriction appears approximately in the middle. Then the cytoplasm in this place bursts, so two separate organisms arise. Each of them contains a core. The contractile vacuole remains in one of the amoebas, and a new one appears in the other. During the day, the amoeba can divide several times. Reproduction occurs in the warm season.

Cyst formation

With the onset of cold weather, the amoeba stops feeding. Its pseudopods are retracted into the body, which takes the shape of a ball. A special protective film is formed on the entire surface - a cyst (of protein origin). Inside the cyst, the organism is in hibernation and does not dry out or freeze. The amoeba remains in this state until favorable conditions occur. When a reservoir dries out, cysts can be carried over long distances by the wind. In this way, amoebas spread to other bodies of water. When warmth and suitable humidity arrive, the amoeba leaves the cyst, releases its pseudopods and begins to feed and reproduce.

Place of amoeba in wildlife

The simplest organisms are a necessary link in any ecosystem. The importance of the common amoeba lies in its ability to regulate the number of bacteria and pathogens on which it feeds. The simplest single-celled organisms eat rotting organic remains, maintaining the biological balance of water bodies. In addition, the common amoeba is food for small fish, crustaceans, and insects. And those, in turn, are eaten by larger fish and freshwater animals. These same simple organisms serve as objects of scientific research. Large accumulations of unicellular organisms, including the common amoeba, participated in the formation of limestone and chalk deposits.

Amoeba dysentery

There are several varieties of protozoan amoebas. The most dangerous for humans is the dysenteric amoeba. It differs from the ordinary one in having shorter pseudopods. Once in the human body, dysenteric amoeba settles in the intestines, feeds on blood and tissues, forms ulcers and causes intestinal dysentery.

Answers to school textbooks

Characteristic structural features of unicellular animals:

Most are microscopic in size;

The body consists of a single cell and is a whole organism with many inherent functions;

The cytoplasm is bounded by a membrane, which may be covered by a cell membrane or shell;

Some species contain several nuclei per cell;

There are organelles of movement - flagella, cilia or pseudopods, which can be temporary or permanent;

The digestive vacuole, formed as a result of pinocytosis or phagocytosis, carries out digestion. The vacuole may be absent in species that absorb nutrients throughout the body surface by diffusion; undigested food remains are thrown out of the vacuole;

The contractile (otherwise called excretory, pulsating, osmoregulatory) vacuole performs an excretory and osmoregulatory function; it is found only in freshwater species;

There are no special respiratory organs; respiration occurs due to the diffusion of gases through the cell surface;

Under unfavorable conditions, they form a cyst (a dense shell is released onto the surface, which allows the cell to be maximally protected from external influences).

2. Prove that the body plan of unicellular organisms corresponds to the general features of the organization of nuclear (eukaryotic) cells.

All eukaryotic cells, both unicellular and multicellular organisms, are characterized by:

The presence of main parts: nucleus, cytoplasm and plasma membrane;

The cytoplasm contains multi-membered organelles that perform special functions: endoplasmic reticulum, Golgi apparatus, mesosomes, ribosomes, mitochondria;

Plastids (in plants and some unicellular organisms), cell center, basal bodies of flagella and cilia;

The cell nucleus is surrounded by a nuclear envelope consisting of two membranes;

Any eukaryotic cell has a cytoskeleton - a system of microtubules and protein fibers that form the internal framework of the cell.

3. What special-purpose organelles are found in unicellular organisms?

In sarcodidae, to move and capture food, if necessary, pseudopods are formed - pseudopodia. They are outgrowths of the cytoplasm reinforced by cytoskeletal fibers.

Flagellates move with the help of one or more flagella, and ciliates move with the help of numerous cilia.

In freshwater species, the excretory and osmoregulatory functions are performed by the contractile vacuole.

In flagellates, the ability to move directionally under the influence of light is due to the activity of the light-sensitive eye - the stigma.

4. Which group of single-celled animals is the most ancient?

The most ancient classes are Flagellates and Sarcodaceae. This is evidenced by the relative simplicity of their organization.

5. Explain the types of nutrition found in flagellates.

According to the method of feeding, flagellates are divided into three groups:

Autotrophic organisms that synthesize organic substances (carbohydrates) using the energy of sunlight, i.e., they feed like real plants (all colored flagellates);

Heterotrophic organisms that use organic substances that have already been created by other organisms (colorless flagellates);

Mixotrophic organisms with a mixed type of nutrition, they are capable of photosynthesis, but also feed on organic substances, absorbing bacteria and other protozoa by phagocytosis (green euglena).

6. Which animals do not have a constant body shape?

Due to the underdeveloped and very mobile skeleton of the cell, formed by protein fibers and microtubules, many sarcoflagellates (for example, amoeba) do not have a constant body shape. In addition, rapid rearrangements of the internal frame make it possible to easily change the shape of the body and quickly form pseudopodia.

7. How do protozoa reproduce?

As a rule, under favorable conditions, single-celled animals reproduce asexually - by cell division, and under unfavorable conditions - sexually.

8. What is the role of protozoa in nature? In human life?

Many protozoa play a significant role in the food chains of a reservoir: they consume bacteria and some algae, and themselves, in turn, serve as food for many invertebrates, fish fry, and tadpoles.

In the seas and oceans, the shells of dead rhizomes, settling to the bottom, form layers of chalk.

9. What are pseudopodia?

Pseudopodia (pseudopods) are organelles of movement. They are outgrowths of the cytoplasm reinforced by cytoskeletal elements.

10. Can protozoans have shells?

Yes. The body of testate amoebae and foraminifera is enclosed in a single-chamber shell equipped with an opening - the mouth, through which pseudopodia emerge into the environment. The shells consist of a chitin-like substance and can have a variety of shapes. Some representatives have purely organic shells, others are impregnated with calcium salts or encrusted with grains of sand.

11. Name the main features of the organization of foraminifera.

Foraminifera are mostly represented by marine rhizomes.

The main features of the foraminiferal organization:

They have a multi-chamber shell consisting of calcium carbonate (due to which their remains form chalk deposits);

Pseudopodia extend from the shell to enable locomotion and capture of food.

12, What protozoa have skeletal structures?

All eukaryotic cells have a cytoskeleton. In some cases it is weakly expressed (as in rhizomes). In other representatives, the cell skeleton ensures the maintenance of a constant body shape throughout the life cycle. The cytoskeleton is most clearly expressed in ciliates. The constant shape of the body is ensured by thick bundles of cytoskeletal fibers adjacent to the membrane.

13. What organisms are called autotrophic?

Organisms that are capable of synthesizing organic substances from inorganic ones are called aetotrophic.

Photosynthetic autotrophs form organic substances (carbohydrates) from carbon dioxide and water using the energy of solar radiation.

Chemosynthetic autotrophs form organic molecules from inorganic ones due to the energy of chemical bonds of inorganic molecules.

14. What are colonies and how do they form in protozoa?

Colonies are large or small collections of cells of single-celled organisms. Colony cells do not have constant specialization. Colonies can be formed as a result of the division of individual cells that do not move away from each other and continue to exist together. Colonies can also form as a result of incomplete cell division, when individuals that have not completely separated from each other remain connected to each other. Colonies differ in both form and method of development. The number of individuals that make up a colony ranges from 4 to 20 thousand cells.