Lecture Notes: Unicellular Organisms - Protists, Archaea, and Bacteria

Overview

• Focus on mostly unicellular organisms: Protists, Archaea, and Bacteria.
• These organisms constitute the majority of living things on Earth.
• All living entities originate from a common ancestor.

Key Evolutionary Differences

• Eukaryotes vs. Prokaryotes
  • "Karyote" refers to nucleus.
  • "Pro" means before; prokaryotes came before the nucleus.
  • Protists: Eukaryotes (have a nucleus).
  • Archaea and Bacteria: Prokaryotes (lack a nucleus).

Archaea

• Oldest known organisms, name reminiscent of "archaic".
• Thrived in Earth's early extreme conditions.
• Extremophiles:
  • Thermophiles: Favor extreme temperatures.
  • Halophiles: Prefer highly saline environments.
  • Methanogens: Produce methane gas.
• Have unique cell walls and membranes distinct from bacteria and protists.

Protista

• "Grab bag" category for unicellular/multicellular eukaryotes not classified as plants, fungi, or animals.
• Commonality: Mostly found in moist or aquatic environments.
• Categories:
  • Photosynthesizing: Related to plants, known as Algae.
  • Non-photosynthesizing: Fungus-like and animal-like.
    • Protozoa: Animal-like, includes amoebas.
    • Fungal-like: Includes slime molds.
• Exhibit diverse nutrient acquisition strategies and movement structures (e.g., cilia, flagella, amoeboid movement).

Bacteria

• Found in diverse environments, including inside and around humans.
• Can be both beneficial and harmful.
• Bacterial Structure:
  • External Structures:
    • Capsule/Slime Layer: Capsule cannot be washed off, slime layer can.
    • Cell Wall: Varies in gram-positive and gram-negative bacteria.
    • Plasma Membrane: Lipid bilayer.
    • Flagella: Prokaryotic, made of flagellin protein, aids in movement (chemotaxis).
    • Fimbriae/Pili: Not all bacteria have them.
  • Internal Structures:
    • Cytoplasm & Ribosomes: Standard cellular components.
    • Nucleoid Area: Contains circular, double-stranded DNA, lacks a true nucleus.
    • Plasmids: Extra DNA, provide genetic advantage.
    • Inclusion Bodies: Store nutrients, important due to lack of membrane-bound organelles.

Conclusion

• Discussed the distinctions between Protista, Archaea, and Bacteria.
• Examined general bacterial structure and functions.