Domains of Life on Earth

Overview of Domains

• All life categorized into three major groups:
  • Domain Bacteria
  • Domain Archaea
  • Domain Eukarya

Characteristics of Domains

• Organisms in each domain share certain characteristics:
  • Similar cell structures
  • Related sequences of ribosomal RNA

Domain Bacteria and Domain Archaea

Prokaryotic Organisms

• Both domains consist of prokaryotic organisms:
  • Single-celled
  • No membrane-bound nucleus

Domain Archaea

• Habitat:
  • Aquatic environments lacking oxygen
  • Extreme conditions: too salty, hot, or acidic
• Indication of ancient heritage:
  • Ability to live in conditions similar to early Earth
• Relevance in Astrobiology:
  • Search for archaean-like organisms on other planets

Domain Bacteria

• Ubiquity:
  • Found in water, soil, atmosphere, human skin, mouth, and intestines
• Role:
  • Some cause diseases; others are beneficial
  • Used in drug manufacturing
  • Important for food processing
  • Support digestive and immune systems

Differences Between Bacteria and Archaea

• Ribosomal RNA studies show they are not closely related
• Cell wall composition:
  • Bacterial Cell Wall: Contains peptidoglycan, protein, polysaccharides, and lipids
  • Archaeal Cell Wall: Lacks peptidoglycan; contains proteins, polysaccharides, and lipids

Domain Eukarya

• Includes eukaryotes:
  • Organisms with a membrane-bound nucleus
• Organelles:
  • Most eukaryotes have internal organelles (e.g., mitochondria, chloroplasts)
• Size:
  • Eukaryotic cells are generally larger than prokaryotic cells

Subdivisions of Domain Eukarya

• Four kingdoms:
  • Protists
  • Plants
  • Fungi
  • Animals