Notes l Kingdom Protista - Class 11 and NEET 2025/2026

 


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)

 Also Read: 

Kingdom Fungi - NOTES

Kingdom Protista - MCQs

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