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The Need for a Transport System

Large multicellular organisms need a specialised transport system because simple diffusion is not fast enough to meet their metabolic needs.Oxygen is needed for respiration and carbon dioxide is a waste product and needs to be removed.The larger the organism, the smaller the surface area to volume ratio.More active organisms have higher metabolic demands. Mammals (endotherms) also have to maintain their body temperature.In summary animals have:
  • high metabolic demands
  • a small surface area to volume ratio
  • molecules such as hormones which are made in one place and used in another
  • food that needs to be digested and the products transported to every cell
  • waste products that need to be removed
  • the need to maintain their body temperature

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Specification: AQA Biology (7401), AS-level, 3.3.4.1 Mass transport in animals. Topic: Mass Transport in Animals.

Key terms in this lesson

diffusion
The net passive movement of molecules or ions from a region of higher concentration to a region of lower concentration, down a concentration gradient.
surface area to volume ratio
The ratio of an organism's or structure's external surface area to its total volume, which decreases as size increases.

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