Protozoa!!! Only third and fourth

Protozoa are simple, single-celled animals. they are the smallest of all animals. most protozoa are microscopic in size, and can only be seen under a microscope. however, they do breathe, move and reproduce like multicelled animals.

there are several types of protozoa. the amoebas are clear, shapeless cells. flagellates have a body shape looking like a hair.

although we can't see them, protozoa do a lot for us. protozoa play a useful role in the food chain as a source of food for fish and other animals. some protozoa are helpful to humans by eating dangerous bacteria. unfortunately, other protozoa are parasites and can be harmful to humans by transmitting disease.