Unicellular Organisms

This lesson covers: 

  1. The difference between unicellular and multicellular organisms
  2. Examples of unicellular organisms

Unicellular organisms versus multicellular organisms

Living things are composed of cells.


Some organisms are unicellular, consisting of a single cell.

Some organisms are multicellular, meaning they are made up of many cells.


Key differences:

  • Unicellular organisms - Consist of one cell that performs all functions necessary for life.
  • Multicellular organisms - Consist of many specialised cells that work together.

Examples of unicellular organisms - Euglena

Euglena are unicellular algae that live in water.

Illustration of Euglena showing nucleus, chloroplast, and flagellum.

Their features include:

  • Nucleus - This manages the cell's activities.
  • Chloroplast - This is the site of photosynthesis.
  • Flagellum - This is used for movement.

Examples of unicellular organisms - Amoeba

Amoebae are unicellular organisms known for their ability to change shape.

Diagram of an amoeba showing the cell membrane, nucleus, and contractile vacuole.

Their features include:

  • Irregular cell membrane - This allows them to alter their shape.
  • Nucleus - This manages the cell's activities.
  • Contractile vacuole - This collects and expels excess water.