Animals Plants Fungi Protists Monerans

Living things show enormous diversity of colour, size, external covering, internal organisation and habitat.

In early classification systems, Man has grouped living things according to the appropriate criteria at that time, e.g. useful, harmful, or neither.

In the 1700s, Swedish taxonomist Carolus Linnaeus classified organisms on the basis of similar structural characteristics. This method is still used today.

The most widely accepted system today, established in 1969 by Whittaker, distinguishes between five major Kingdoms of living things: Animals, Plants, Fungi, Protists and Monera.

(Note: see Animals, Plants and Fungi? - A simplified classification system for more details of these groups.)

Animals

• Are heterotrophs, cannot make food by photosynthesis and therefore need to consume other organisms for food.
  
  
• Are usually able to move about.
  

Are made up of many complex eukaryotic cells. In these cells, the chromosomes are located in a nucleus separated from the cytoplasm by a nuclear membrane, creating a specialised organelle with a specific role. Other membrane-bound organelles have other specialised roles (see Animal cells). Most reproduce sexually.

Plants

Are able to produce their own food by photosynthesis. Do not move about by their own motion. Are made up of many complex eukaryotic cells containing a nucleus and specialised organelles, as well as a cellulose cell wall. Reproduce sexually.

Fungi

• Do not make their own food but absorb nutrients from other organisms.
  
  
• Do not move about.
  
  
• Mostly consist of many cells.
  
  
• Cells are complex (eukaryotic) with nucleus and specialised organelles, as well as a cellulose cell wall.
  
  
• Often can reproduce sexually, and asexually with spores.
  

Protists
(e.g. single-celled organisms such as Amoeba)

• Are mostly single-celled microscopic organisms, except for the algae, which are also usually placed in this group.
  
  
• The cells are complex (eukaryotic) with nucleus and specialised organelles, but some also have a cellulose cell wall.
  
  
• Some can make their own food: others eat microscopic organisms for food.
  
  
• Reproduce by cell division (asexual reproduction), but sexual reproduction also occurs through the exchange of some genetic material between the two organisms.
  
  
• Some Protists were formerly classified as single-celled plants if they had cell walls and could photosynthesise, but many could move as well.

Current practice is to group these in the Kingdom Protista due to their simple structure and method of reproduction, although not all biologists agree on this.

Monerans
Also referred to as Procaryotes (e.g. bacteria)

• These differ from all other living things in their lack of internal specialisation at the cellular level.
  
  
• These procaryotic cells do not have the chromosomes surrounded by a nuclear membrane, but the strands of DNA are simply present within the cytoplasm. There are no other organelles surrounded by membranes, but all life functions still occur. These cells are less specialised, therefore less efficient.
  

Some photosynthesise; others need to eat. They reproduce by cell division. Are single-celled or colonial (group of cells co-existing).

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