Why do large organisms need a transport system?
1.All organisms need to exchange materials between themselves and their environment.
2.In small organisms this exchange can occur over the surface of their body.
3.However, with increasing size, the surface area to volume ratio decreases to the point where the needs of the organism cannot be met by the body surface alone. Need specialist exchange surfaces.
4.In larger and more complex multicellular organisms, the tissues & organs have become more specialised & dependent on one another- this makes a transport system all the more essential.
Whether or not there is a specialised transport system, and whether or not it is circulated by a pump depends on 2 things:
1.The surface area to volume ratio
(the lower the surface area to volume ratio the greater the need for a specialised transport system)
2. The activity of the organism
(the more active the organism the greater the need for a specialised transport system)
Features of transport systems
1.A suitable medium to carry materials
(usually liquid & water based due to water readily dissolving substances)
2. A form of mass transport- bulk movement over large distances
A closed system of tubular vessels that contain the transport medium that form a branching network to reach all parts of the organism.
3. A mechanism for moving the transport medium within vessels. This requires a pressure difference between one part of the system and another- this is achieved in 2 ways:
a)Muscle contraction- body muscles or pumping organ.
b)Means to control the direction of flow of the medium- e.g. Valves
No comments:
Post a Comment