Exchange between organisms and their enviroment

Question 1

Environment around the cells

Answer 1

Tissue fluid

Question 2

Two ways that exchange takes place

Answer 2

Osmosis/Diffusion
Active transport

Question 3

Surface area to volume ratio

Features

Answer 3

+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.

Question 4

Features of specialised exchange surfaces.

Answer 4

-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