Domain - GCSE Biology Definition

In GCSE Biology, the term 'Domain' refers to one of the highest levels of classification in the biological world. It's used to group all living things into three major categories: Bacteria, Archaea, and Eukarya. Bacteria are single-celled organisms without a nucleus; Archaea are also single-celled but have different cell structures and live in extreme environments; and Eukarya includes all organisms with complex cells, like plants, animals, and fungi, which have a nucleus. This system helps scientists organise and understand the diversity of life on Earth.