Overview
of Kingdom Protista
Kingdom Protista includes all single-celled eukaryotes. The boundaries of this kingdom
are not well-defined, making classification sometimes subjective. Protists are
primarily aquatic and form a link with plants, animals, and fungi. Protistan
cells have a well-defined nucleus and membrane-bound organelles. Some have
flagella or cilia. Protists reproduce both asexually and sexually.
Key Groups in Protista:
1
Chrysophytes
- Includes: Diatoms and
golden algae (desmids)
- Habitats: Freshwater and
marine environments
- Characteristics:
- Microscopic and float passively
(plankton)
- Mostly photosynthetic
- Diatoms have silica-embedded cell
walls forming two thin overlapping shells
- Importance: Diatoms
contribute to diatomaceous earth, used in polishing and filtration. They
are chief producers in oceans.
2
Dinoflagellates
- Habitat: Mostly marine
- Characteristics:
- Photosynthetic, varying in color
(yellow, green, brown, blue, red) due to different pigments
- Cell wall with stiff cellulose
plates
- Two flagella: one longitudinal,
one transverse
- Phenomena: Rapid
multiplication can cause red tides (eg, Gonyaulax), releasing toxins that
can kill marine life
3
Euglenoids
- Habitat: Freshwater,
stagnant water
- Characteristics:
- Protein-rich flexible layer called
pellicle instead of a cell wall
- Two flagella (one short, one long)
- Photosynthetic in sunlight,
heterotrophic in darkness
- Example: Euglena
4
Slime Moulds
- Lifestyle: Saprophytic
- Characteristics:
- Move along decaying matter
engulfing organic material
- Form a large aggregation called
plasmodium under favorable conditions
- During adverse conditions, form
fruiting bodies with spores
- Spores: Have true walls,
are resistant, and dispersed by air currents
5
Protozoans
·
Lifestyle: Heterotrophs, live as predators or parasites
·
Classification: Four major groups
o
Amoeboid
Protozoans:
- Habitat: Freshwater, seawater,
moist soil
- Movement: Use pseudopodia (false
feet)
- Examples: Amoeba, Entamoeba
(parasitic)
o
Flagellated
Protozoans:
- Free-living or parasitic
- Movement: Use flagella
- Example: Trypanosoma (causes
sleeping sickness)
o
Ciliated
Protozoans:
- Aquatic, actively moving with
cilia
- Have a cavity (gullet) that opens
to the outside, directing food into the gullet
- Example: Paramoecium
o
Sporozoans:
- Infectious spore-like stage in
their life cycle
- Example: Plasmodium (causes malaria)
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