CLASSIFICATION OF PROTOZOA

 

 CLASSIFICATION OF PROTOZOA

 CLASSIFICATION OF PROTOZOA

All protozoal species are assigned to the kingdom Protista in the Whittaker classification. The protozoa are then placed into different groups primarily on the basis of how they move. The groups are called Phyla or Classes. Member of the four major groups is Mastigophora, Sarcodina, Apicomplexa and Ciliophora.

CHARACTERISTICS OF PROTOZOA.

MOTILITY

Protozoa are notable for their ability to move independently, a characteristic found in the majority of species. They usually lack the capability for photosynthesis, although the genus euglena is renowned for motility as well as photosynthesis (and is therefore considered both an alga and a protozoan). Although most protozoa reproduce by asexual methods, sexual reproduction has been observed in several species. Most protozoal species are aerobic, but some anaerobic species have been observed in the human intestine and animal rumen.

ENVIRONMENTAL FACTORS AND FOOD CHAIN

Protozoa are located in most moist habitat. Free living species inhabit freshwater and marine environments and terrestrial species inhabit decaying organic matter. Some species are parasites of plants and animals.

Protozoa play an important role as zooplankton, the free floating aquatic organism of the ocean. Here, they are found at the bases of many food chains and they participate in many food webs.

SIZE AND SHAPE.

Protozoa vary substantially in size and shape. Smaller species may be the size of fungal cells; larger species may visible to the unaided eye. Protozoa cells have no cell walls and therefore can assume infinite variety of shapes. Some genera have cells surrounded by hard shells, while the cells of other genera are enclosed only in a cell membrane.

Many protozoa alternate between a free-living vegetative form known as trophozoite and a resting form known as cyst. The protozoa cyst is somewhat analogues to the bacteria spore hence it resists harsh conditions in the environment. Many protozoa parasites are taken into the body in the cyst form. Most protozoa hace a single nucleus, but some have both a macronucleus and one or more micronuclei. Contractile vacuoles may be present in protozoa to remove excess water and food vacuoles are often observed.

NUTRITION AND LOCOMOTION.

Protozoa are heterotrophic microorganisms(meaning they cannot produce their own food), and most species obtain large food particles by phagocytosis. The food particle is ingested a food vacuole. Lysosomal enzymes then digest the nutrients in the particle and the products called cytostomes, through which particles pass in phagocytosis. Many protozoa species move independently by one of three types of locomotor organelles: flagella, cilia and pseudopodia. How a protozoan move is an important consideration assigning it to a group.