KINGDOM-PROTISTA
Kingdom—Protista includes all single-celled eukaryotes but
the boundries of this kingdom are not well-defined. This
kingdom was first proposed by Ernst Haeckel (1866).
Physiologically, kingdom—Protista acts as a connecting link
between the kingdom—Monera and the complex
multicellular kingdoms—Fungi, Plantae and Animalia.
Kingdom—Protista includes the following categories such
as dinoflagellates, chrysophytes, euglenoids, slime moulds
and protozoans.
The general characteristic features of kingdom—Protista are
given below
(i) These are mostly aquatic organisms. Some protists
also live in the bodies of animals as parasites.
(ii) The cells are eukaryotic. These contain membrane
bound cell organelles like mitochondria, Golgi
complex, endoplasmic reticulum, 80 S ribosomes, etc.
(iii) Locomotion may either occur by pseudopodia
(Amoeba, Euglypha), cilia (Paramecium),
wriggling (sporozoans, non-flagellates) and
mucilage propulsion (some protists like diatoms).
Diatoms do not have any organelles for locomotion.
(iv) Protists show various modes of nutrition such as
(a) Photosynthetic (Holophytic) Dinoflagellates,
diatoms and euglenoids.
(b) Holozoic (Zootrophic) Protozoans like Amoeba
and Paramecium.
(c) Saprobic (Saprotrophic) In slime moulds.
(d) Parasitic Trypanosoma, Giardia. Plasmodium,
Entamoeba.
(e) Mixotrophic In Euglena.
(f) Symbiotic In zooflagellates like
Trichonympha and Lophomonas.
(g) Pinocytosis In Amoeba to absorb soluble organic
substances.
(v) Most of the protists are aerobic. However, some
protists that live at the bottom of aquatic habitats
can respire anaerobically.
(vi) Protists reproduce asexually and sexually by a
process involving cell fusion and zygote formation.
The major groups of Protista are
(a) Protistan algae (photosynthetic protists)
(b) Slime moulds (consumer-decomposer protists).
(c) Protozoan protists.