Protista — The Protest Kingdom

Protists are mostly unicellular eukaryotic organisms (cells have membrane-bound nuclei). They are placed in Kingdom Protista — a "catch-all" group for organisms that don't fit neatly into plants, animals, or fungi.

Key distinction from bacteria: Protists have a true nucleus; bacteria are prokaryotic (no nucleus membrane).

1. Protozoa (animal-like protists)

Heterotrophic — consume other organisms. Motile using pseudopodia, flagella, or cilia.

2. Algae (plant-like protists)

Autotrophic — photosynthesise using chlorophyll.

1. Pseudopodia extend toward food
2. Prey engulfed by phagocytosis → food vacuole forms → digestion
3. Reproduces by binary fission
4. Under stress: forms cyst (protective wall)

• Cilia for movement and feeding
• Oral groove funnels food to cytostome (cell mouth)
• Conjugation: temporary fusion for genetic exchange
• Contractile vacuoles: expel excess water (osmoregulation)

• Protists = eukaryotic + mostly unicellular (distinct from bacteria = prokaryotic)
• Euglena: mixotrophic — has chloroplasts but also ingests food
• Paramecium: cilia + two nuclei + contractile vacuoles
• Amoeba: pseudopodia + phagocytosis + binary fission + cyst
• Plasmodium → malaria is a protist disease, not bacterial/viral

1. What is the key difference between protists and bacteria?
2. Name the mode of locomotion in Amoeba.
3. Why is Euglena considered both plant-like and animal-like?
4. Which protist causes malaria and what is its vector?
5. Stretch: Why do freshwater protists have contractile vacuoles but marine ones often don't?