Exchange Surfaces and Breathing Revision Notes
Exchange Surfaces
Exchange Systems
-small organisms – 1 cell thick – do not need a specialised exchange system as they rely on diffusion of O2 and CO2 and have a low metabolic
activity
-large organisms – more than 2 layers of cells – need a specialised exchange system as diffusion is not effective (too long and slow)
-3 factors affecting the need for exchange systems:
-size -surface area to volume ratio -level of activity
Size
-all cells need oxygen and nutrients to survive and remove waste products
-small organisms (single celled) cytoplasm close to environment so they survive on diffusion
-multi-cellular organisms have a long diffusion pathway which is too slow and ineffective to the innermost cells
Surface Area to Volume Ratio (SA:Vol)
-small organisms – small surface area and small volume. SA is large compared to volume so a large ratio. SA large enough to supply cells
-larger organisms – larger surface area, larger volume. Increasing volume increases is quicker SA. Low SA:Vol ratio.
-some organisms can change shape to get a large SA:Vol ratio (e.g. flatworm)
-smaller SA:Vol ratio, diffusion will be less effective.
-when vol > SA, diffusion will be less effective.
Level of Activity
-more active organisms have increased metabolic activity which needs oxygen and nutrients to supply the energy for movement
Features of Good Exchange Surface
-Large Surface Area – more space to pass through (folded membranes) [e.g. root hair cell in plants]
-Thin Permeable Barrier – reduces diffusion distance and allows substances through [e.g. alveoli in lungs]
-Good Blood Supply – brings fresh supplies and removes waste: needs a high concentration gradient [e.g. vessels in human tissue]
-Ventilation to Maintain Diffusion Gradient – helps make diffusion more efficient [e.g. ventilation in the gills of a fish ensures a flow of water)
Working Out SA:Vol
Circle
Radius (r) (mm) Surface Area (4πr2) (mm2) Volume (4/3πr2) (mm3) SA:Vol
1 12.5 4.2 3:1
2 50.2 33.5 1.5:1
5 314.2 523.6 0.6:1
Cube
Length (cm) Surface Area (6 x 1 face) (cm2) Volume (h x w x d) (cm3) SA:Vol
1 1 1 1:1
2 4 8 1:4
5 10 125 1:12.5
Exchange Surfaces
Exchange Systems
-small organisms – 1 cell thick – do not need a specialised exchange system as they rely on diffusion of O2 and CO2 and have a low metabolic
activity
-large organisms – more than 2 layers of cells – need a specialised exchange system as diffusion is not effective (too long and slow)
-3 factors affecting the need for exchange systems:
-size -surface area to volume ratio -level of activity
Size
-all cells need oxygen and nutrients to survive and remove waste products
-small organisms (single celled) cytoplasm close to environment so they survive on diffusion
-multi-cellular organisms have a long diffusion pathway which is too slow and ineffective to the innermost cells
Surface Area to Volume Ratio (SA:Vol)
-small organisms – small surface area and small volume. SA is large compared to volume so a large ratio. SA large enough to supply cells
-larger organisms – larger surface area, larger volume. Increasing volume increases is quicker SA. Low SA:Vol ratio.
-some organisms can change shape to get a large SA:Vol ratio (e.g. flatworm)
-smaller SA:Vol ratio, diffusion will be less effective.
-when vol > SA, diffusion will be less effective.
Level of Activity
-more active organisms have increased metabolic activity which needs oxygen and nutrients to supply the energy for movement
Features of Good Exchange Surface
-Large Surface Area – more space to pass through (folded membranes) [e.g. root hair cell in plants]
-Thin Permeable Barrier – reduces diffusion distance and allows substances through [e.g. alveoli in lungs]
-Good Blood Supply – brings fresh supplies and removes waste: needs a high concentration gradient [e.g. vessels in human tissue]
-Ventilation to Maintain Diffusion Gradient – helps make diffusion more efficient [e.g. ventilation in the gills of a fish ensures a flow of water)
Working Out SA:Vol
Circle
Radius (r) (mm) Surface Area (4πr2) (mm2) Volume (4/3πr2) (mm3) SA:Vol
1 12.5 4.2 3:1
2 50.2 33.5 1.5:1
5 314.2 523.6 0.6:1
Cube
Length (cm) Surface Area (6 x 1 face) (cm2) Volume (h x w x d) (cm3) SA:Vol
1 1 1 1:1
2 4 8 1:4
5 10 125 1:12.5
