Circulatory system of a mammal


Why large organisms have a transport system:

  • Surface area to volume ratio decreses to a point where the needs of the organism cannot be met by the body surface alone
  • Required to absorb nutrients and respiratory gases
  • Remove excretory products
  • Exchange systems located in specific regions of the organism
  • Transport system is required to take materials from cells to exchange surfaces and from exchange surfaces to cells
  • Materials have to be transported between exchange surfaces and the environment and also need to be transported between different parts of the organism
  • As organisms have evolved into larger and more complex structures, the tissues and organs of which they are made have become more specialised and dependent upon one another

Whether or not there is a specialised transport medium, and whether or not it is circulated by a pump depends on two factors -

  • The surface area to volume ratio
  • How active the organism is

Features of transport systems:

  • A suitable medium in which to carry materials - for example blood
  • A form of mass transport in which the transport medium is moved around in bulk over large distances - more rapid than diffusion
  • A closed system of tubular vessels that contains the transport medium and forms a


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