6.1: Exchange between organisms + their environment Flashcards
Tissue fluid
The environment around the cells of multicellular organisms.
Examples of things that need to be exchanged between an organism and its environment
respiratory gases
nutrients
excretory products
heat
Passive exchange process
and examples
No metabolic energy is required
eg: diffusion and osmosis
Active exchange process
and example
Metabolic energy is required
eg: active transport
For exchange to be effective:
The exchange surface(s) of an organism must be large compared with its volume
As organisms become larger their volume…
increases at a larger rate than their SA
Organisms have evolved
1 or both of these features
A flattened shape so that no cell is ever far from the surface.
Specialised exchange surfaces with large SAs to increase the SA:V ratio.
Example of organisms with a flattened shape
2
flatworm or leaf
Examples of organisms with specialised exchange surfaces
2
lungs in mammals
gills in fish
When calculating the SA:V of cells assume…
The cells have uniform shape
Features of specialised exchange surfaces
5
A large SA:V ratio which increases with rate of exchange.
Very thin so short diffusion distance.
Selectively permeable allows selected materials to cross.
Movement of the environmental medium to maintain a diffusion gradient.
A transport system to ensure the movement of the internal medium
Diffusion equation
= SA x difference in conc. / length of diffusion pathway
