Protozoa are single-celled organisms without cell walls. This diverse group of over 65,000 species generally share these basic attributes. Traditionally, however, protozoa are considered primitive unicellular animals : hence their name, union of the Greek words protos, “first,” and zoo, “animal.” This is because they are heterotrophic (they must consume organic matter) and are endowed with voluntary movement . Protozoa [pro″to-zo´ah] a subkingdom (formerly a phylum) comprising the unicellular eukaryotic organisms; most are free-living, but some lead commensalistic, mutualistic, or parasitic existences. Their body lacks a periplast. They are single-celled heterotrophic eukaryotes, which eat bacteria and other food sources. Also question is, what is protozoa in simple words? Protozoa (also protozoan, plural protozoans) is an informal term for single-celled eukaryotes, either free-living or parasitic, which feed on organic matter such as other microorganisms or organic tissues and debris. It was first coined in the 1800s. Most of the time, protozoans are microscopic, and only a few of them grow big enough to be seen by the naked … The word protozoa comes from the word protos, which was Greek for "first," and zoia which meant "animal." Protozoa are small (but not simple) organisms. Therefore, they may be naked or covered by a calcareous shell. They are single-celled heterotrophic eukaryotes, which eat bacteria and other food sources. However, 'protozoa' is often used for convenience, especially in junior education. Diseases Caused By Protozoa: Literally meaning “first animals“, protozoans are considered to be one of the very first organisms to thrive in the planet. See more. Basically, they are multicellular organisms and have membrane-bound organelles that work independently from the whole cell.. Protozoa definition, a major grouping or superphylum of the kingdom Protista, comprising the protozoans. It is a rather convenient hold-all term, but actually 'protozoa' are classified in a number of different phyla. They are believed to be a part of the microbial world as they are unicellular and microscopic. It is an old term, and the wider term protist is generally preferred today. They usually lack flagella and have temporary protoplasmic outgrowths called pseudopodia for locomotion. Protozoa are non-phototrophic, unicellular, eukaryotic microorganisms with no cell walls. Additionally, what is protozoa in simple words? There is a great deal to know about their classification, characteristics and more. Protozoa are notable for their ability to move independently, a characteristic found in the majority of species. They are unicellular, jelly-like protozoa found in fresh or sea water and in moist soil. Protozoa are single-celled eukaryotes (organisms whose cells have nuclei) that commonly show characteristics usually associated with animals, most notably mobility and heterotrophy. Before then, the microscopic protozoa, defined by their organelles, were unable to be fully appreciated. Protozoa are small (but not simple) organisms.