2.3 Kingdom Classification: Protista

Characteristics of Kingdom Protista

• Unicellular: Most are single-celled.
• Eukaryotic: Possess a true nucleus and membrane-bound organelles.
• Nutrition: Can be autotrophic (photosynthetic), heterotrophic (ingestive/absorptive), or mixotrophic.
• Locomotion: May have flagella, cilia, or pseudopods.
• Habitat: Primarily aquatic (freshwater, saltwater, moist terrestrial).

Amoeba: Basic Structure

• Irregular Shape: Lacks fixed shape, changes due to pseudopods.
• Cell Membrane: Outer boundary.
• Cytoplasm: Ectoplasm (outer, clear), Endoplasm (inner, granular).
• Nucleus: Single, large, dense, controls activities.
• Contractile Vacuole: Regulates water balance (osmoregulation).
• Food Vacuoles: Contain ingested food particles.

Amoeba: Life Processes

• Nutrition (Holozoic): Ingestion (pseudopods engulf food) → Digestion (food vacuole + lysosomes) → Absorption → Assimilation → Egestion.
• Locomotion: Moves by pseudopods (false feet).
• Respiration: Through general body surface (diffusion of O₂/CO₂).
• Excretion: Waste removed by diffusion; contractile vacuole expels excess water.
• Reproduction:
  • Binary Fission: Under favorable conditions, splits into two identical daughter cells.
  • Multiple Fission (Encystment): Under unfavorable conditions, forms a protective cyst; nucleus divides repeatedly, forming many small Amoebae (pseudopodiospores).