Date & Time : 18, January 2021 02:22
General Characteristics of Protista
- Protists are microscopic, unicellular and eukaryotic organisms.
- Their size commonly range from 10 to 52 micrometers, but they can grow as large as 1 mm, and are seen easily by a microscope.
- Many protists are free Living, found in fresh and salt water; but a number of protists are endoparasites causing pathogenic effects in their hosts.
- Body is surrounded by a thin plasma membrane which may be covered by pellicle (a thin layer supporting the cell membrane).
- They may be naked organisms or enclosed in a shell.
- The cytoplasm is differentiated into an outer ectoplasm and inner endoplasm.
- Protistans possess pseudopodia, cilia or flagella as the locomotory organelles.
- Nutrition may be holophytic, holozoic, saprozoic or parasitic.
- Respiration occurs by the diffusion of gases through body surface.
- Reproduction may take place by asexual or sexual means.
- Asexual reproduction takes place by the process of binary fission, multiple fission, sporulation or budding.
- Sexual reproduction takes place by conjugation (syngamy), endomixis, automixis, cytomixis or hemixis.
A Few Examples
SCIENTIFIC NAME- Noctiluca.
GEOGRAPHICAL DISTRIBUTION- Commonly found in madras, atlantic and pacific oceans
HABITAT-Marine and pelagic.
- large circular body measuring about 1-1.5mm in diameter.
- body is covered by a stout pellicle.
- A small flagellum and a long,stout tentacle is present.
- Mouth is elongated having a pouch like cytopharynx.
- Nucleus is single and large.
- Cytoplasm is highly vacuolated and differentiated into ectoplasm and endoplasm.
- Asexual reproduction by binary fission and spore formation.
Euglena is cosmopolitan in distribution.
It is found in freshwater ponds,ditches,lakes and slow running streams rich in organic matter.
- It is oval,spindle shaped measuring about 50-100 microns in length.
- Body is blunt anteriorly and pointed posteriorly.
- Single whip like fllagelum arises from the base of reservoir.
- Body is covered by striated and flexible pellicle.
- Anterior end of body bears a small funnel like cytostome and a tubular cytopharynx which leads into a large spherical reservoir.
- Nucleus is large and spherical located toward the posterior region.
- Cytoplasm is differentiated into ectoplasm and endoplasm.
- Nutrition is holophytic or saprophytic.
- Reproduction is asexual by binary fission.
Found all over the world.
Commonly found in mud, freshwater ponds, ditches, slow running streams.
- Irregular shaped body(measuring about 0.25 mm-1 mm in diameter) appears like a colourless mass of protoplasm.
- Body is covered by a thin, clear, elastic and semi-permeable plasma membrane called plasmalemma.
- Cytoplasm is distinguished into ectoplasm and endoplasm.
- Endoplasm contains a spherical nucleus, a large contractile vacuole and various food vacuoles.
- Locomotion by short and blunt pseudopodia.
- Asexual reproduction by binary fission.
HABITAT-Freshwater ponds,pools,ditches,streams,lakes,reservoirs and rivers.
Specially abundant in ponds rich in organic matter.
- Slipper shaped body about 0.3mm in length.
- Cilia are uniformly arranged in longitudinal rows except at posterior end of the body.
- On the oral side is a groove ,the oral groove or peristomial groove, running backwards obliquely to the right side of anterior end to about middle of the body.
- This groove ends in mouth or cytostome.
- Locomotion by lashing of cilia.
- Body is covered y pellicle.
- Cytoplasm is clearly distinguishale into ectoplasm and endoplasm.
- Ectoplasm contains basal granules.
- Endoplasm contains two nuclei(large macronucleus,small micronucleus),two contractile vacuoles and reserved food materials.
- Asexual reproduction is by transverse binary fission,sexual reproduction is by conjugation,endomixis,autogamy and hemixis.
SCIENTIFIC NAME- Vorticella
GEOGRAPHICAL DISTRIBUTION-Cosmopolitan in distribution.
HABITAT-Freshwater ponds , lakes , rivers , streams attached to some objects like weeds.
- Inverted bell shaped body with a long, slender stalk for attachment.
- Rim of bell is thick and surrounded by cilia.
- Cilia are arranged in two circles,in an outer anticlockwise fashion on the rim and in inner one on the edge of disc.
- Body consists of pellicle,ectoplasm and endoplasm .
- Endoplasm contains a long horse shoe shaped macronucleus ,a small micronucleus,a single contractile vacuole and food vacuoles. medulla.
- Free broad end of the body is oral and the opposite end is aboral.
- Reproduction by binary fission and conjugation.