Three-Domain System - GCSE Biology Definition

The Three-Domain System is a way of classifying all living things on Earth into three major groups called domains: Bacteria, Archaea, and Eukarya. Bacteria and Archaea are both made up of prokaryotic, single-celled organisms, but they differ in their genetic material, cell wall structure, and other cell components. The Eukarya domain includes all organisms with complex cells that contain a nucleus, such as plants, animals, fungi, and humans. This system helps scientists understand the relationships between different types of organisms by grouping them based on shared characteristics. It was introduced by the scientist Carl Woese to better reflect the diversity of life on Earth.