Overview
This lecture covers the three domains of life—Bacteria, Archaea, and Eukarya—based on cellular organization and structure.
The Three Domains of Life
- All living organisms are classified into three domains: Bacteria, Archaea, and Eukarya.
- Classification is based on differences in cellular organization and structure.
Bacteria
- Bacteria are single-celled organisms with a distinct cellular structure.
- Bacteria are a main focus in microbiology due to their diversity and importance.
Archaea
- Archaea are single-celled organisms similar to bacteria but have different cell walls.
- Often called "prehistoric bacteria," but are distinct from true bacteria.
- Archaea are less frequently discussed in general biology courses.
Eukarya
- Eukarya includes all organisms with eukaryotic cells (cells with a nucleus).
- Eukaryotes are grouped into animals, plants, fungi, and protists.
- Humans belong to the animal group within Eukarya.
- Protists include all eukaryotes that are not animals, plants, or fungi.
- Protists matter in microbiology, especially single-celled organisms like algae and protozoa.
Key Terms & Definitions
- Domain — the highest taxonomic rank, grouping all life into Bacteria, Archaea, or Eukarya.
- Bacteria — single-celled prokaryotes with unique cellular structures.
- Archaea — single-celled prokaryotes with distinct cell walls, separate from bacteria.
- Eukarya — domain of organisms with eukaryotic cells (nucleus-containing).
- Protist — eukaryotic organisms not classified as plants, animals, or fungi (includes algae and protozoa).
Action Items / Next Steps
- Review examples of organisms from each domain.
- Read more about the distinguishing features of Bacteria, Archaea, and Eukarya.