BIology 13.5 Circulatory System of a Mammal

Why large organisms need a transport system

All organisms need to exchange materials between them and their environment.

When size increases, surface area to volume ratio decreases - needs of organism can't be met by diffusion and body surface alone.

A specialised exchange system is needed - absorbs nutrients and respiratory gases and removes excretory products.

A transport system is needed - takes materials from cells to exchange surfaces and back.

Materials need to be transported between exchange surfaces and the environment and then transported to different parts of the organism.

Tissues are therefore more specialised and depend upon one another.

Whether there is a specialised transport medium and/or a pump to circulate it depends on:

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

The lower the surface area to volume ratio and more active the organism is = greater need for specialised transport medium.

Features of transport systems

• Suitable medium in which to carry materials - e.g. blood…