Lecture Notes: Protists, Archaea, and Bacteria

Introduction

Focus on mostly unicellular organisms: protists, archaea, and bacteria.
These organisms make up most of the living things on Earth.
All living things stem from a common ancestor. Key evolutionary split between eukaryotes and prokaryotes.

Eukaryotes.
Diverse organisms, either unicellular or multicellular that do not fit into the categories of plants, fungi, or animals.
Common Environment: Moist or aquatic environments.
Categories:
- Photosynthesizing protists (Algae).
- Non-photosynthesizing protists (related to fungi and animals):
  - Protozoa (e.g., amoebas).
  - Fungus-like (e.g., slime molds).
Unique adaptations for obtaining nutrients and movement structures (e.g., cilia, flagella, amoeboid movements).

Prokaryotes, among the oldest organisms (name akin to 'archaic').
Adapted to extreme environments (extremophiles):
- Thermophiles: Thrive in extreme temperatures.
- Halophiles: Thrive in salty environments.
- Methanogens: Produce methane gas.
Unique cell walls and membranes distinct from bacteria and protists.

Also prokaryotes.
Found in diverse environments, including inside other organisms (e.g., human gut).
Can be both beneficial and harmful.
Structure:
- Capsule/Slime Layer: External protection, slime layers can be washed off, capsules cannot.
- Cell Wall: Differentiates between gram-positive and gram-negative bacteria.
- Plasma Membrane: Lipid bilayer.
- Flagella: For movement (made of protein flagellin, different from eukaryotic flagella). Enables chemotaxis.
- Fimbriae/Pili: Small projections, not present in all bacteria.
- Internal Structures:
  - Cytoplasm and Ribosomes: Standard cell components.
  - Nucleoid: Region for the chromosome (not a true nucleus, no membrane).
  - Circular DNA: Double-stranded DNA in bacterial chromosomes, along with plasmids for extra genetic traits.
  - Inclusion Bodies: Storage for nutrients, crucial due to absence of membrane-bound organelles.