What is the role of protozoa in nature, in human life?

The simplest are unicellular animals, the only cell of which performs all the functions, character for an independent organism. The habitat of the protozoa is soil, water, plants, animals. Science knows about 70 thousand species of protozoa. Among them are both extremely useful, such as plankton, which feeds many marine animals, and parasites that cause various diseases. All species of protozoa are important for nature, since they play their specific role in all ecosystems and take part in the cycle of substances in the Earth’s biosphere, and are also food for many animals.