The variety of protozoa. Types, characteristics and meaning of protozoa

The most primitive representatives of the animal kingdom are unicellular organisms. They form a vast type of protozoa, the variety of which we will consider today. The Latin name for this type is Protozoa. Because unicellular organisms are difficult to divide into animals (Protozoa) and plants (Protophyta), they are often combined into the Protista group. The variety of protozoa is striking. Their number is more than 30 000 species, and most of them are invisible to the naked eye, because in size they are no larger than the tip of the needle. Let's briefly describe the variety of protozoa.

Brief characteristics of protozoa

All these organisms are divided into 4 classes, depending on the mode of movement. Sarcodina moves due to pseudopodia; These same basically free-living organisms capture prey. Flagellar (Mastigophora) are moved by one or more flagella. Sporozoa (Sporozoa), including Plasmodium sp., Are parasitic forms devoid of special locomotor devices. Infusoria (Ciliata) unite basically free-living forms, which are moved with the help of cilia. Similar to the miniature tube of the infusorian Stenior, feeding, is attached to the surface of aquatic plants.

Like all other animals, protozoa are generally mobile, they feed on a variety of chemically complex foods. In their body, it is split, supplying it with energy. The whole variety of protozoa needs an aquatic environment. Although most of the species live either in the sea or in fresh water, a lot of them lead a parasitic lifestyle in the organisms of higher animals, including humans, where they are often the cause of a variety of diseases. The variety of pathogenic protozoa is great.

Flagellae

To flagellates belong two genus - Euglena and Chlamydomonas, whose representatives contain chlorophyll and, consequently, are capable of photosynthesis. This also includes the flagellar flagellates (Dinoflagellata), dressed in a cellulose capsule and included in the plankton. In man lives, causing a sleeping sickness, a parasitic form of Trypanosoma (pictured below).

Sarkode

Sarkodovye - another group, which includes a large number of species. All this variety of protozoa is difficult to characterize, so let's say a few words about the most famous. All of us are familiar with the representative of sarcodogs from the school, like the free living Amoeba proteus (pictured below). Amoeba is a unicellular animal belonging to a vast type of protozoa that thrive everywhere where it is humid enough.

Their sizes range from microscopic parasites of Babesia blood to large foraminifers, whose shells are 5 cm in length.

Luchiviki, sunflowers and sporoviki

Radiolarians (Radiolaria) and sunflowers (Heliozoa) possess a skeleton of silica. Therefore, they are sometimes collected and used as an abrasive. Falling out from the general rule of variability, sporoviki demonstrate a high degree of homogeneity, which does not differ all the variety of protozoa. Parasitic protozoa are all their kinds. Therefore sporoviki are deprived of organelles necessary for movement and nutrition: they do not need to move, and they digest food they have already digested. Their life cycle combines stages that reproduce both asexually and sexually, resulting in spores that can produce many hundreds of individuals.

Infusoria-shoe

Paramecium (infusoria-shoe) is a specialized unicellular animal. It is worth to tell about it, characterizing the variety of water protists. The outer layer of cell contents - ectoplasm - is bounded by a dense shell carrying a multitude of tiny cilia. Their rhythmic concerted strokes allow the animal to move. Pericroma leads to blind growth - pharynx, surrounded by granular endoplasm. Nutritional particles enter the throat due to movements of the cilia, and then fall into the vacuoles. The contents of the digestive vacuoles moving in the endoplasm are digested by enzymes. Undigested residues are thrown out through the powder. Water balance is maintained through the operation of two pulsating vacuoles. Of the two nuclei, the larger (macronucleus) is associated with the metabolism in the cell, and the smaller (micronucleus) is involved in the sexual process.

Plasmodium vivax

Let us consider another known form, characterizing the variety of protozoa. Parasitic protozoa are numerous, but this malignant pathogen gives a lot of trouble to people. Plasmodium vivax, getting into the bloodstream of a person after being bitten by his female Anopheles mosquito, penetrates into the liver cells where it multiplies. When the infected cells are ruptured, the plasmodium leaves and infects new ones. Then it is repeatedly introduced into erythrocytes, multiplying in them and destroying. Finally, male and female sex cells (gametocytes) appear. Getting with blood in the next mosquito, male gametocytes are divided in his stomach, forming gametes. From the product of their fusion, the zygote, new plasmodia appear that penetrate the salivary glands of the mosquito. And the cycle repeats.

Reproduction of protozoa

With asexual reproduction the protozoans divide in half, forming two individuals. This division of fully formed cells captures both protoplasm and the nucleus. As a result, two identical daughter cells are formed. Under adverse conditions, some flagellates and sarcods secrete a dense, impermeable protective shell (cyst) within which the cell can divide. If it falls into favorable conditions, the cyst is destroyed, and individuals reproducing asexually appear.

The methods of sexual reproduction of protozoa are very diverse. Paramecium, for example, multiplies by conjugation: two individuals belonging to different lines merge laterally, and then, after dividing the nuclei and exchanging nuclear material, diverge. Later, both partners can share, producing up to eight (four from each) of children with kernels with mixed heredity. Amoeba, multiplying asexually, is divided into two daughter cells. They have the same value. At the beginning of the division in the nucleus, which becomes shorter and thicker, chromosomes appear; Each consists of two chromatids. The pulsating vacuole is divided, and its halves diverge. At the same time, the chromatids divide, and the cytoplasm begins to be doubled. With the end of the division of chromosomes, the cytoplasm also separates. The resulting daughter cells are identical.

Eating Protozoa

Like other animals, the simplest receive energy by eating complex organic compounds. Amoeba sp. Captures pseudopodia food particles, and they are digested in the digestive vacuoles with the participation of enzymes. Paramecium sp. Lives mainly due to bacteria, driving them in the cirrus movements of cilia. Trichonympha sp. Lives in the intestine of termites and feeds there those substances that are not absorbed by the host. Acineta sp. (Pictured below) use only certain types of infusoria, which sometimes are larger than themselves.

Movement

Protozoa move in three basic ways. Sarkodovye "crawl" through the formation of protoplasm outgrowths. The movement is created due to the directionality of the endoplasmic current in one direction and its reversible transformation at the periphery into a gelatinous ectoplasm. Due to sharp impacts of the flagellum, flagellates move. Infusoria move with the help of many tiny, wavering cilia.

Bacteria and viruses

General characteristics and variety of protozoa should be supplemented with a short story about bacteria and viruses, which are often confused with them. They give a lot of trouble to a person, but they play a special role in nature. Bacteria and viruses are the smallest organisms on the planet. Although these are relatively simple organized beings, they can not be called primitive. They are able to survive in very unfavorable conditions, and the great ability to adapt to changed conditions puts them on a par with the most advanced and prosperous forms. Viruses are not cells, so they can not be attributed to unicellular, but bacteria can be considered as such. However, they are not the simplest, since they do not have a nucleus. Let's talk about them in more detail.

Where do bacteria live?

Unlike viruses, bacteria are cells. However, they are much simpler than those of highly organized creatures, and vary greatly in size and shape. Bacteria are found everywhere. They can live even under conditions that exclude the existence of more complex organisms. They are met in the ocean even at a depth of 9 km. When the environmental conditions worsen, the bacteria form a stable resting stage - the endosporium. This is the most stable of known living organisms: some endospores do not die even when boiling.

Of all possible habitats, the most risky is another organism. Bacteria get into it usually through wounds. But, having penetrated inside, they must resist the defenses of their victims, especially against phagocytes (cells that can capture and digest them) and antibodies that can neutralize their harmful effects. Therefore, some bacteria are surrounded from the outside by a mucous membrane, invulnerable to phagocytes; Others after capture by phagocytes can live in them; Finally, the third develop masking substances that help them to hide their presence in the affected cells, and the latter do not produce antibodies.

Harmful and beneficial bacteria

Bacteria can cause harm in three ways: for example, blockage of various vital channels in the body due to the multiplicity; The release of toxic substances (the toxin of the soil bacterium Clostridium tetani (pictured below), causing tetanus, is one of the strongest poisons known to science); As well as stimulation of allergic reactions in the victims.

Antibiotics have been effective against microbial infections for some time, but many bacteria have developed resistance to a number of drugs. They multiply rapidly, sharing in favorable conditions every 10 minutes. At the same time, naturally, the chances for the appearance of mutants resistant to certain antibiotics are increasing. But not all bacteria living in other organisms do harm. So, in the gastrointestinal tract of a cow, a sheep or a goat, there is a special department - a scar in which many bacteria live, which help animals digest vegetative fiber.

Mycoplasma

Mycoplasmas - the smallest of all cellular organisms and, possibly, a transitional stage between viruses and bacteria - are found naturally in wastewater, but can also afflict animals, causing them to have such diseases as, for example, some forms of arthritis in pigs.

The importance of bacteria

Due to these organisms corpses are decomposed, and the organic substances contained in them are returned to the soil. Without this constant cycle of organic building blocks, life could not exist. A person widely uses the vital activity of bacteria to convert organic waste and raw materials into useful products when composting, making cheeses, oils, vinegar.

Finally

As you can see, the variety and meaning of protozoa is great. Despite the fact that their size is very small, they play an important role in maintaining life on our planet. Of course, we only briefly described the variety of protozoa. We hope you had a desire to get to know them better. Systematics and the variety of protozoa are an interesting and extensive topic.