EXCHANGE Flashcards
What is exchange
the transfer of materials between two environments
Why are most cells not able to use diffusion
they are too far from exchange surfaces
What does the mass transport system do
maintains the diffusion gradients that bring materials to and from the cell-surface membranes
What affects the amount of each material that is exchanged
the size and metabolic rate of an organism
What are examples of materials that need to be interchanged between an organism and its environment (4 points)
1) respiratory gases
2) nutrients
3) excretory products
4) heat
What 2 ways can exchanges take place, and what takes neither
1) passively
2) actively
heat
What is passive exchange
no metabolic energy required
What are examples of passive exchange
diffusion and osmosis
What is active exchange
metabolic energy required
What is an example of active exchange
active transport
What 2 adaptations have organisms made to increase the rate of exchange
1) flattened shape so no cell is far from the surface
2) specialised exchange surfaces with large areas to increase the SA:V
What characteristics do specialised exchange surfaces have (5 points)
1) large SA:V
2) very thin so the diffusion distance is short and therefore exchange is rapid
3) selectively permeable to allow selected materials to cross
4) movement of the environmental medium (e.g. air) to maintain a diffusion gradient
5) transport system to ensure the movement of the internal medium (e.g. blood) to maintain a diffusion gradient
How do you calucate diffusion
(surface area X difference in concentration) / length of diffusion pathway
Why are specialised exchange surfaces often located inside an organism
they are thin ; so easily damaged and dehydrated
