Eukaryotes and Prokaryotes

The cell is the smallest significant unit of all living organisms; it is the basic building block of all living things. Every tissue and organ of the body is made up of cells.

Each cell contains specialised structures inside, called organelles, which carry out particular tasks that help the cell function as a whole.

All cells are either eukaryotic or prokaryotic.

Eukaryotic Cells

In eukaryotic cells, genetic information (DNA) is enclosed within a nucleus. This is what defines them.

Diagram of a eukaryotic cell showing the nucleus, cell membrane, mitochondria cytoplasm, rough endoplasmic reticulum, smooth endoplasmic reticulum, secretory vesicle, ribosome and golgi apparatus

Eukaryotic cells vary in size. They typically have a diameter between 10 and 100 μm.

  • All animal and plant cells are eukaryotic

Prokaryotic Cells

In a prokaryotic cell, the genetic material is not enclosed within a nucleus. Instead, it is a single loop of DNA in the cytoplasm. There can also be smaller rings of DNA, which are called plasmids.

  • Prokaryotic cells are much smaller than eukaryotic cells, many being less than 1 µm in size.

Prokaryotic cells have cytoplasm, an outer cell membrane and a cell wall. However, do not confuse a bacterial cell wall with a plant cell wall.

Diagram of a prokaryotic cell showing the capsule, cell wall, plasma membrane, nucleoid region, chromosome, fimbriae, pilus, plasmid, cytoplasm, ribosome and flagellum
  • Currently, all known prokaryotes, such as bacteria and archaea, are single-celled organisms.

Some prokaryotic cells may contain a flagellum, which helps them to move around. Multiple flagellum are called flagella.