Eukaryotes are organisms whose cells have a membrane-bound nucleus. All animals, plants, fungi, and many unicellular organisms are eukaryotes. They are the basis for both unicellular and multicellular organisms. Eukaryotic cells contain several membrane-bound structures, or organelles, which are specialized cellular subunits that carry out specific cellular functions. Some of the key characteristics of eukaryotic cells include:

• Nucleus: Eukaryotic cells have a nucleus enclosed within the nuclear membrane. The nucleus contains a single, linear DNA, which carries all the genetic information.

• Organelles: Eukaryotic cells contain organelles, including mitochondria (cellular energy exchangers), a Golgi apparatus (secretory device), an endoplasmic reticulum (a canal-like system of membranes within the cell), and lysosomes (digestive apparatus within many cell types) .

• Size: Eukaryotes are organisms that range from microscopic single cells, such as picozoans under 3 micrometres across, to animals like the blue whale, weighing up to 190 tonnes and measuring up to 33.6 metres (110 ft) long, or plants like the coast redwood, up to 120 metres (390 ft) tall.

Eukaryotic cells are different from prokaryotic cells, which do not have a membrane-bound nucleus.