Introduction
The word protist is derived from the Greek word "promise" which means "very first". The protists are the very first eukaryotes, much more complex than prokaryotes. There is a vast variety of aquatic eukaryotes that have different morphology, reproductive systems, types of nutrition, life lifestyles and have evolved from prokaryotes.
Fungi are non-motile, achlorophyllos, spore-bearing organisms with chitin-containing cell walls, and live either parasitic, saprophytic, or symbiotic modes of life.
7.1 Protists: The Evolutionary Relationship
Protists were the very first eukaryotes to evolve. They include all unicellular eukaryotes and some simple multicellular organisms of diverse groups. They can not be considered fungi, animals, or plants. They are a polyphyletic group and belong to many tribes.
They exhibit similarities and differences with plants (such as autotrophic unicellular and multicellular algae), fungi (heterotrophic slime molds and water molds), and heroic animals (protozoans). Thus they do not share a single common ancestor. Margalis and Schwartz have listed 27 phyla, to place this diverse assemblage of organisms. Their size varies from
microscopic protozoans and unicellular algae to very large brown algae Kelps more than 60 meters in length. Most protists are unicellular, some simple multicellular (without specialized tissues) and few are colonial (ie., a loose aggregation of cells). Some protists are coenocytes which are multinucleated cells but not multicellular
How do protists get their nutrients?
Some protists are plant-like autotrophic (photosynthetic algae), some are Ingestive heterotrophs like animals (protozoans and slime molds) and some are fungi Ske absorptive heterotrophs (water molds)
Different modes of life:
Some protists are free-living (Amocha, Paramecium), and many are symbiotic either mutualist (Trichonympha and Colonympha) or parasitic (Plus) Most are aquatic (either freshwater or marine algae). They also make up a part of the plankton, (can not resist water current, Le, floating) none of these are nekton (which can resist water care, can swim against water current).
How do protists reproduce?
All protists exhibit asexual reproduction, and many also reproduce sexually (exhibit mess and syngamy, ie, the fusion of gametes). Mest dost contain multicellular sex organs. There is no embryo or blastula sages in protists.
Types of locomotion:
Few are sessile while most are motile at some stage of their life, locomote either by pseudopodia (b) or flagella (Euglena) or cilia (Parameci). Some have two or more means of locomotion (ie both flagella and pseudopodia).
Many protists (especially algae) are palatable thus they are the most abundant source of food for animals and human
Evolution of Protists:
All protists have evolved from prokaryotes (Monera) while fungi, plants, and animals have evolved from protists. Some protists like Euglena and slime mold exhibit characters of
plants, animals, and fungi
7.2 Major Groups of Protists
The Protists are placed in the following major groups protozoans, algae, Myxomycota, and cocoa. The salient features of these groups are given below.
7.2.1 Protozoa: The Animal-like protists
Protozoans are animal-like unicellular protists that ingest food and have no cell wall. The word protozoan is derived from two Latin words "Proto" means first "Zoan" means animal.
They are polyphyletic groups with the following salient features. Habitat: Mostly aquatic (either freshwater or marine such as actinopods, and foraminifera). Many are parasitic, e... Trypanorama. Plasmon Extec Their body is a single mass of protoplasm with almost all cellular structures of a typical cell, within which it performs all features of life such as nutrition, locomotion," reproduction, respiration, excretion, homeostasis, etc.
The vacuoles in protozoans are either for ingestion, digestion, and egestion (such as food vacuoles) or in freshwater species contractile vacuoles for excretion (removal of water and nitrogenous wastes).
Reproduction:
Both sexual and sexual reproduction take place
Locomotion:
Either by cilia (Paramecin), flagella (Trypano), or pseudopodia (mob) while most parasitic forms have no locomotory organelles (Plasmodium) Many protons can regenerate and form to overcome unfavorable conditions.
It is believed that probably animals have evolved from protozoans because both groups are motile, ingestive heterotrophs and do not possess cell walls.
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