Unicellular organisms are considered the most primitive representatives of the animal kingdom. They form an extensive type of protozoa, the diversity of which we will consider today. The Latin name for this type is Protozoa. Since unicellular organisms are difficult to separate into animals (Protozoa) and plants (Protophyta), they are often combined into a 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, since they are no larger than the tip of a needle in size. Let us try to briefly characterize the variety of protozoa.
Brief description of protozoa
All these organisms are divided into 4 classes, depending on the method of movement. Sarcodina (Sarcodina) move due to pseudopodia; by them, these mostly free-living organisms capture prey. Flagella (Mastigophora) are moved by one or more flagella. Sporozoa (Sporozoa), including Plasmodium sp., Are parasitic forms devoid of special locomotor devices. Ciliates (Ciliata) combine mainly free-living forms that move with the help of cilia. Similar to a miniature tube, the St older infusoria, eating, attaches to the surface of aquatic plants.
Like all other animals, protozoa are usually mobile, they feed on a variety of chemically complex foods. In their body, it breaks down, supplying it with energy. All the variety of protozoa needs an aquatic environment. Although most of the species live either in sea or in fresh water, a lot of them lead a parasitic lifestyle in organisms of higher animals, including humans, where they are often the cause of various diseases. The variety of pathogenic protozoa is great.
Flagellum
Flagellates include two genera - Euglena and Chlamydomonas, representatives of which contain chlorophyll and, therefore, are capable of photosynthesis. This also includes carapace flagellates (Dinoflagellata), dressed in a cellulose capsule and included in plankton. In a person living, causing sleeping sickness, the parasitic form of Trypanosoma (pictured below).
Sarcode
Sarcodes are another group that 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. We are all familiar from the school with such a representative of sarcodes as the free-living Amoeba proteus (in the photo below). Amoeba is a unicellular animal belonging to the 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.
Rays, sunstrokes and sporozoans
Rays (Radiolaria) and sunstrokes (Heliozoa) have a silica skeleton. Therefore, they are sometimes collected and used as an abrasive material. Falling out of the general rule of variability, sporozoans demonstrate a high degree of homogeneity, which does not differ in all the variety of protozoa. Parasitic protozoa are all of their species. Therefore, sporozoans are deprived of the organelles necessary for movement and nutrition: they do not need to move around, and they digest already digested food. Their life cycle combines stages that reproduce both asexually and sexually, resulting in the formation of spores that can produce many hundreds of individuals.
Infusoria shoe
Paramecium (ciliates-shoe) is a specialized unicellular animal. It is certainly worth talking about, characterizing the variety of aquatic protozoa. The outer layer of the cell contents - ectoplasm - is bounded by a dense membrane that carries many tiny cilia. Their rhythmic coordinated beats allow the animal to move. The peristome leads into a blind outgrowth - the pharynx surrounded by granular endoplasm. Food particles enter the throat due to the movements of the cilia, and then enter the vacuole. 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 activity 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
Consider another well-known species, characterizing the variety of protozoa. Parasitic protozoa are numerous, but this causative agent of malaria is especially troublesome to people. Plasmodium vivax, entering the bloodstream of a person after being bitten by a female Anopheles mosquito, penetrates the liver cells, where it multiplies. When the affected cells rupture, the plasmodium comes out and infects new ones. Then it is repeatedly introduced into erythrocytes, multiplying in them and destroying. Finally, male and female germ cells (gametocytes) appear. Getting with blood in the next mosquito, male gametocytes divide in his stomach, forming gametes. From the product of their fusion - zygotes - new plasmodiums appear, penetrating the salivary glands of the mosquito. And the cycle repeats.
Simple breeding
With asexual reproduction, protozoa divide in half, forming two individuals. Such division of fully formed cells captures both protoplasm and the nucleus. As a result of this, two identical daughter cells are formed. In adverse conditions, some flagella and sarcodes secrete a dense, impermeable protective membrane (cyst), inside which the cell can divide. When it enters into favorable conditions, the cyst is destroyed, and individuals appear that reproduce asexually.
Methods of sexual reproduction of protozoa are very diverse. Paramecium, for example, multiplies by conjugation: two individuals belonging to different lines merge sideways, and then, after fission of nuclei and exchange of nuclear material, diverge. Later, both partners can share, producing up to eight (four from each) daughter individuals with nuclei with mixed heredity. Amoeba, propagating asexually, is divided into two daughter cells. They have the same size. At the beginning of fission in the nucleus, which becomes shorter and thicker, chromosomes appear; each consists of two chromatids. The pulsating vacuole divides, and its halves diverge. Chromatids diverge at the same time, and the cytoplasm starts lacing in half. With the end of chromosome division, the cytoplasm is also divided. The resulting daughter cells are identical.
Nutrition of the simplest
Like other animals, protozoa receive energy by feeding on complex organic compounds. Amoeba sp. captures food particles with pseudopodia, and they are digested in digestive vacuoles with the participation of enzymes. Paramecium sp. lives mainly due to bacteria, driving them into the feathery movements of the cilia. Trichonympha sp. lives in the intestines of termites and feeds on those substances that are not absorbed by the host. Acineta sp. (in the photo below) use only certain types of ciliates for food, which are sometimes larger than themselves.
Movement
Protozoa move in three main ways. Sarcodes creep by the formation of protoplasm outgrowths. The movement is created due to the direction in one direction of the endoplasmic current and its reversible transformation on the periphery into a gelatinous ectoplasm. Due to the sharp blows of the flagellum, the flagella move. Ciliates move with the help of many tiny vibrating cilia.
Bacteria and viruses
The general characteristics and variety of protozoa should be complemented by a brief account of the bacteria and viruses that are often confused with them. They cause a lot of trouble to humans, but play a special role in nature. Bacteria and viruses are the smallest organisms on the planet. Although these are relatively simple organized beings, you cannot call them primitive. They are able to survive in very adverse conditions, and their great ability to adapt to changing conditions puts them on a par with the most advanced and successful forms. Viruses are not cells, so they cannot be classified as unicellular, but bacteria can be considered as such. However, they are not the simplest because they do not have a kernel. We will tell you more about them.
Where bacteria live
Unlike viruses, bacteria are cells. However, they are much simpler to construct than the cells of highly organized creatures, and vary greatly in size and shape. Bacteria are found everywhere. They can live even under conditions that preclude the existence of more complex organisms. They are met in the ocean even at a depth of 9 km. When environmental conditions worsen, the bacteria form a stable resting stage - the endospore. This is the most stable of the known living organisms: some endospores do not die even when boiled.
Of all the possible habitats, the most risky is another organism. Bacteria usually enter it through wounds. But, having penetrated inside, they must resist the defenses of their victim, especially against phagocytes (cells that can capture and digest them) and antibodies that can neutralize their harmful effects. Therefore, some bacteria are surrounded externally by a mucous membrane that is invulnerable to phagocytes; others, after being captured by phagocytes, can live in them; finally, others produce masking agents that help them hide their presence in the affected cells, and the latter do not produce antibodies.
Harmful and beneficial bacteria
Bacteria can be harmful in three ways: for example, by blocking various vital channels in the body due to multiplicity; the release of toxic substances (the toxin of the soil bacteria Clostridium tetani (pictured below), which causes tetanus, is one of the most powerful poisons known to science); as well as stimulation of allergic reactions in victims.
Antibiotics were effective against microbial infections for some time, but many bacteria have developed resistance to a number of drugs. They multiply rapidly, sharing under favorable conditions every 10 minutes. In this case, of course, the chances of the appearance of mutants that are resistant to certain antibiotics increase. But not all bacteria living in other organisms do harm. So, in the gastrointestinal tract of a cow, sheep or goat, there is a special section - a scar, in which many bacteria live, helping animals digest plant fiber.
Mycoplasmas
Mycoplasmas - the smallest of all cellular organisms and, possibly, a transitional stage between viruses and bacteria - are found naturally in wastewater, but can also affect animals, causing diseases such as, for example, some forms of arthritis in pigs.
The value of bacteria
Thanks to these organisms, corpses decompose, and the organic substances contained in them return to the soil. Without this constant cycle of organic building blocks, life could not exist. Man makes extensive use of the vital activity of bacteria to turn organic waste and raw materials into useful products in composting, the manufacture of cheeses, butter, and vinegar.
Finally
As you can see, the diversity and significance 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 diversity of the simplest animals. We hope you have a desire to get to know them better. The taxonomy and variety of protozoa is an interesting and extensive topic.