KINGDOM : PROTISTA
All unicellular eukaryotes, irrespective of their mode of nutrition, are included in the kingdom Protista in Whittaker’s system. The term protista was coined by Ernst Haeckel. This kingdom forms a link between kingdom Monera on one hand and other three kingdoms i.e., Plantae, Fungi and Animalia on the other hand. Protistans are ancestors of all multicellular eukaryotes (plants, fungi and animals ).
General Characteristics of Protista
- Unicellular, eukaryotic organisms. Some are colonial without much cellular differentiation. Organization at tissue level is absent.
- Mostly aquatic organisms.
- Cell structure is eukaryotic type having all kinds of membrane bound organelles and 80 S cytoplasmic ribosomes and cell may possess cellulosic cell wall.
- Flagella and cilia have (9+2) pattern of microtubule organization consisting of tubulin protein.
- Movement by pseudopodia, flagella or cilia where cilia where ciliary mode is fastest.
- Mode of nutrition may be photosynthetic (holophytic), holozoic (ingestive), saprobic or parasitic (absorptive). Some have mixotrophic nutrition (photosynthetic and saprobic) as in Euglena.
- Reproduction occurs by asexual and sexual means
- Life cycle is of 2 types – i) Showing zygotic meiosis ii) Showing gametic meiosis.
- These are decomposers, photosynthetic or parasites. Parasitic protists may cause diseases like dysentery, malaria, sleeping sickness etc.