Eukaryote

Definition

Any organism whose cells contain a membrane-bound nucleus and other membrane-bound organelles, constituting the domain Eukarya. Eukaryotes include animals, plants, fungi, and diverse unicellular groups such as amoebae, ciliates, and flagellates. This cellular architecture distinguishes them from prokaryotes (Bacteria and Archaea), which lack internal membrane systems. In entomology and arachnology, all insects, arachnids, and other arthropods are eukaryotes, as are their parasites (many protozoa, fungi, and nematodes) and symbionts.

Etymology

From Greek eu- (true, good) + karyon (nut, kernel), referring to the true nucleus.

Example

The honey bee Apis mellifera is a eukaryote whose cells contain a nucleus with 16 chromosomes, mitochondria for aerobic respiration, and a complex endomembrane system—features absent in its bacterial gut symbionts such as Snodgrassella alvi.

Synonyms

• eucaryote

Related Terms

• Prokaryote
• Nucleus
• organelle
• mitochondrion
• domain
• cell membrane
• endosymbiosis

Usage Notes

Used as both noun (an organism) and adjective (eukaryotic cell). Contrast with prokaryote is fundamental in biology; the distinction predates but aligns with the three-domain system of life. Some biologists prefer 'eucaryote' spelling, though 'eukaryote' dominates. The term encompasses extraordinary diversity—yeasts, diatoms, kelp, mushrooms, nematodes, beetles, and whales are all eukaryotes—so additional descriptors are usually needed in specific contexts.