6.1 Exchange between
organisms and their
environment
,Why do organisms need to
exchange with their environment?
• In order to maintain their metabolic rate, they need to source the
reactants for metabolic reactions
• e.g. respiration needs glucose and oxygen
• High metabolic rate = exchange more material
• They use a mass transport system and have exchange surfaces –
unless the organisms is very small, it will have an exchange surface
other than its outer surface e.g. skin, because the diffusion distanc
will be too large
,What needs to be exchanged [and
how?]
• Respiratory gases [e.g. O2]
• Nutrients [e.g. glucose]
• Excretory products [e.g. CO2]
• Heat
• Except for heat, these things can be exchanged passively by
diffusion/osmosis or actively by active transport
, Surface area to volume ratio
• For exchange to be effective, the surface area of the exchange surf
must be large compared to the volume of the organism
• Small organisms have a large surface area compared to their volum
so they don’t need a specialised exchange surface
• Large organisms have lower surface area to volume ratios so the
diffusion distance between their surface and their inner cells is too
high and they cannot use their skin/surface as an adequate method
exchange. They adapt:
• Flattened shape
• Specialised exchange surfaces with large surface areas
organisms and their
environment
,Why do organisms need to
exchange with their environment?
• In order to maintain their metabolic rate, they need to source the
reactants for metabolic reactions
• e.g. respiration needs glucose and oxygen
• High metabolic rate = exchange more material
• They use a mass transport system and have exchange surfaces –
unless the organisms is very small, it will have an exchange surface
other than its outer surface e.g. skin, because the diffusion distanc
will be too large
,What needs to be exchanged [and
how?]
• Respiratory gases [e.g. O2]
• Nutrients [e.g. glucose]
• Excretory products [e.g. CO2]
• Heat
• Except for heat, these things can be exchanged passively by
diffusion/osmosis or actively by active transport
, Surface area to volume ratio
• For exchange to be effective, the surface area of the exchange surf
must be large compared to the volume of the organism
• Small organisms have a large surface area compared to their volum
so they don’t need a specialised exchange surface
• Large organisms have lower surface area to volume ratios so the
diffusion distance between their surface and their inner cells is too
high and they cannot use their skin/surface as an adequate method
exchange. They adapt:
• Flattened shape
• Specialised exchange surfaces with large surface areas
