Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The Three-Domain System was proposed by Carl Woese in 1990, dividing all cellular life forms into three domains: Archaea, Bacteria, and Eukarya.
The classification is based on the nucleotide sequence of the (ribosomal RNA) genes, which are highly conserved across different species.
Domain Archaea: Includes primitive prokaryotes such as Methanogens, Halophiles, and Thermoacidophiles. Their cell walls lack peptidoglycan, and their membranes contain branched-chain lipids linked by ether bonds instead of ester bonds.
Domain Bacteria: Includes true bacteria (Eubacteria) such as Cyanobacteria and Mycoplasma. Their cell walls contain peptidoglycan (-acetylglucosamine and -acetylmuramic acid), and they possess ribosomes.
Domain Eukarya: Includes all eukaryotic organisms characterized by membrane-bound organelles and a true nucleus. This domain is divided into four kingdoms: Protista, Fungi, Plantae, and Animalia.
The 6-Kingdom Classification system is derived from these three domains, where Kingdom Monera is split into Kingdom Archaebacteria (Domain Archaea) and Kingdom Eubacteria (Domain Bacteria).
📐Formulae
💡Examples
Problem 1:
An organism is isolated from a hot spring with a temperature of . It lacks peptidoglycan in its cell wall and contains branched-chain hydrocarbons in its membrane. Identify its domain and possible kingdom.
Solution:
Domain: Archaea; Kingdom: Archaebacteria.
Explanation:
Extremely thermophilic organisms that lack peptidoglycan and possess ether-linked branched lipids are characteristic of the Domain Archaea.
Problem 2:
Contrast the cell membrane chemistry between Domain Bacteria and Domain Archaea.
Solution:
Bacteria: Phospholipids with ester-linked straight-chain fatty acids; Archaea: Ether-linked branched-chain hydrocarbons (isoprenoids).
Explanation:
The ether linkage in Archaea is more stable at extreme and temperature than the ester linkage found in Bacteria and Eukarya.