Exchange between organisms and their enviroment Flashcards
Environment around the cells
Tissue fluid
Two ways that exchange takes place
Osmosis/Diffusion
Active transport
Surface area to volume ratio
Features
+For exchange to be effective, the exchange surface of the organism must be large compared to the volume.
+Organisms have evolved some features to increase exchange effectiveness
- A flattened shape o that no cell is ever far from the surface
-Specialised exchange surfaces with large S.A to increase S.A to V ratio.
Features of specialised exchange surfaces.
-A Large S.A relative to the volume of the organism which increases the rate of exchange
-Very thin so that the diffusion distance is short and therefore materials cross the exchange surface rapidly.
-Selectively permeable to allow selected materials to cross.
-Movement of the environmental medium, for example air to maintain a concentration gradient.
-A transport system to ensure the movement of the internal medium. eg blood to maintain a concentration gradient.
Diffusion ∝ SA x Difference in conc / Length of
diffusion path