Biology-2-tissues, organs and organ systems..

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Cell organisation:

Large multicellular organisms have different systems inside them for exchanging and transporting materials.

For example...

mammals have a breathing system- this includes the airways and lungs. The breathing system is needed to take air into and out of the lungs, so that oxygen and carbon dioxide can be exchanged between the body and the enviroment.

Exchange systems are made up of specialised cells. The process by which cells become specialised for a particular job is called differentiation. Differentiation occurs during the development of a multicellular organism. 


A tissue is a group of similar cells that work together to carry out a particular function.

A tissue can include more than once type of cell. Mammals (like humans) have several different types of tissue:

  • Muscular tissuewhich contracts(shortens) to move whatever it is attached to.
  • Glandular tissuewhich makes and secretes substances like enzymes(proteins that control chemical reactions) and hormones(chemical messengers.)
  • Epithelial tissue- which


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