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An '''animal''' is any creature which is a member of the Animalia kingdom. Animals must eat [[plant]]s or other organisms to survive. The plants are called "producers" and the animals are "consumers". Scientists call consumers [[heterotroph]]s. Animals have complex [[eukaryotic cell]]s, unlike bacteria which have much simpler [[prokaryote|prokaryotic]] cells.  Animal cells do not have [[cell wall]]s, only structural [[protein]]s in the [[cell membrane]]; this allows the animal cell a certain amount of flexibility.

An '''animal''' is any creature which is a member of the [[Animalia]] kingdom. Animals must eat [[plant]]s or other organisms to survive. The plants are called "producers" and the animals are "consumers". Scientists call consumers [[heterotroph]]s. Animals have complex [[eukaryotic cell]]s, unlike bacteria which have much simpler [[prokaryote|prokaryotic]] cells.  Animal cells do not have [[cell wall]]s, only structural [[protein]]s in the [[cell membrane]]; this allows the animal cell a certain amount of flexibility.

The simplest of all animals are [[sponge]]s, which do not move.  Sponges have different cells for different tasks, but these cells are not organized further into [[tissue]]s or [[organ]]s.  Sponges also do not exhibit [[symmetry]], unlike all other animals.

The simplest of all animals are [[sponge]]s, which do not move.  Sponges have different cells for different tasks, but these cells are not organized further into [[tissue]]s or [[organ]]s.  Sponges also do not exhibit [[symmetry]], unlike all other animals.