state that Archaea and Bacteria are prokaryotes and that there are differences between them, limited to differences in membrane lipids, ribosomal RNA and composition of cell walls

Published by Patrick Mutisya · 14 days ago

Cambridge A-Level Biology 9700 – Classification

Classification – Prokaryotes

Learning Objective

State that Archaea and Bacteria are prokaryotes and describe the three main differences between them:

  • Membrane lipid composition

  • Ribosomal RNA (rRNA) sequence

  • Composition of the cell wall

Key Points

Both Archaea and Bacteria lack a membrane‑bound nucleus and other membrane‑bound organelles, which classifies them as prokaryotes. Despite this similarity, they differ in several fundamental biochemical features.

Comparative Table

FeatureArchaeaBacteria
Membrane lipidsEther‑linked isoprenoid chains (branched)Ester‑linked fatty acids (unbranched)
Ribosomal RNA (16S rRNA)Distinct sequence; groups with eukaryotes in phylogenetic treesDistinct sequence; groups with other bacteria
Cell‑wall compositionOften pseudo‑peptidoglycan or S‑layer proteins; no true peptidoglycanPeptidoglycan (murein) layer is a defining feature

Why These Differences Matter

  1. They reflect separate evolutionary lineages despite superficial similarity.

  2. They influence the organisms’ ecological niches and resistance to extreme conditions.

  3. They are the basis for laboratory identification and classification.

Suggested diagram: Comparative schematic of archaeal and bacterial cell envelopes highlighting lipid types, rRNA location, and cell‑wall structure.