A large number and wide distribution characterize unicellular animals as animals that play a significant role in nature. Free-living protozoa occupy an important place in the circulation of substances in the biosphere. Aquatic protozoa constitute the main part of plankton, they are used for food by larger animals. Many, feeding on suspended organic particles and bacteria, play an essential role in the biological purification of waters. Protozoa participate in the processes of soil formation. Marine sarcodes played a very important role in the formation of sedimentary rocks: many limestones are composed largely of shells of foraminifera. Radiolarian silt is formed from the skeletons of the rays in the ocean floor, from which the silica rocks form over time. Some types of fossil foraminifera
Of great importance is a group of protozoa that are human parasites. About 30 species cause dangerous protozoal diseases. So, dysenteric amoeba, inhabiting the human large intestine, causes a serious disease – amoebiasis, the symptoms of which are similar to dysentery. The source of infection is a sick person, allocating a large number of cysts to the environment. Infection of water sources, food products, vegetables, fruits promotes the spread of amoebic dysentery. In the human intestine, other protozoans can live: flagellates – lamblia, infusoria balantidium. Severe diseases cause some types of sporoviks. For example, malarial plasmodia, being in human blood, destroy red blood cells. There are 4 types of malarial plasmodia that cause various forms of malaria. A characteristic feature of this disease are regularly recurring attacks of debilitating fever with increasing temperature. Often the disease ends with the death of a person. The carrier of the pathogen of malaria is the malarial mosquito, in whose organism the plasmodia pass a part of its life cycle. Currently, foci of malaria persist in some tropical regions
– in South Asia, South America, Africa. The heavy protozoal diseases of man include sleeping sickness, the pathogens are flagellates – trypanosomes, and various forms of leishmaniasis caused by other flagellar leishmanias.