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the need for exchange surfaces 3.1.1 - Coggle Diagram
the need for exchange surfaces 3.1.1
cell need to exchange… with their surrounding enviroment
into
glucose
mineral ions
O2
water
out of
water
urea
CO2
hormones (& other proteins)
3 main factors effecting need for an exchange system
SA:V ratio
level of activity
size
Size
in unicellular organism all cytoplasm is very close to environment they live in so diffusion will supply enough O2 & nutrients to keep cells alive & active
multicellular organisms have several layers of cells so O2 & nutrients diffusion into them have longer diffusion pathway
diffusion is too slow to enable sufficient supply to innermost cells
SA:V ratio
small organisms = large SA:V ratio therfore exchange can take place over surface of the body - don't need a specialised exchange system
larger organisms = smaller SA:V ratio therefore need specialised surface for exchange of substances with their environment (e.g. gills & lungs)
the smaller he cell/organism the higher the SA:V ratio so the faster the rate of diffusion
calculating SA:V ratio
surface area of cube = 6a^2
volume of cube = a^2
surface area of sphere = 4π r^2
volume of sphere = 4/3π r^3
divide the surface area by the volume to find the SA:V ratio (SA:V ratio should always be expresses as a ratio to 1 - volume always 1)
Level of activity
some organisms are more active than others
metabolic activity uses energy from food & requires O2 to release energy in aerobic respiration
cells of an active organism need good supply of nutrients & O2 to supply the energy for movement - this need for energy is increased in animals, such as mammals that keep themselves active
Exchange & transport systems
to meet grater demands, larger multicellular organism need efficient & specialised;
exchange surfaces - villi (& microvilli) in small intestine for absorption of digested nutrients; alveoli in lungs for gas exchange; root hair cells in plant to absorb water & dissolved minerals
transport systems - circulatory system & respirator system in mammals; xylem & phloem in plants
