Surface area : volume ratio Flashcards
Exchange surfaces
The structure that exchange of substances between external environment and internal environment
External environment
Outside a cell/ organism
Includes lumen outside a cell in a multicellular organism
Internal environment
Inside a cell/organism
What must substances cross to truly enter or leave a cell/organism?
Cell surface membranes
Immediate external environment for cells in multicellular organism
Tissue fluid
Mass transport systems
Carry substances between exchange surfaces and the rest of the body/ between parts of the body
Relationship between organism and surface area:volume ratio
As size of organism increases, the surface area to volume ratio DECREASES
Why do smaller organisms not need mass transport systems?
Have more surface area:volume ratio so can exchange enough substances directly with their environment, enough to maintain their metabolism
Short diffusion pathways to centre so quicker for substances to directly diffuse to centre
What do large organisms with a small surface area to volume ratio + longer diffusion pathways have?
Adaptations to have mass transport systems to facilitate exchange of susbtances
Relationship between structure of organism and surface area: volume ratio
Having shorter diffusion pathways (due to being thick or large organism) reduces surface area to volume ratio
Relationship between metabolic rate and size of organisms
Bigger organisms (per kg of body mass) have reduced metabolic rate
Why do larger organisms ahave a reduced metabolic rate?
They have a smaller surface area to volume ratio
So cannot lose heat as FAST
So reduce metabolic reactions to avoid overheating because these reactions release heat
Problem with overheating
Denatures proteins because hydrogen bonds/ ionic bonds/ disulfide bridges in tertiary structure break thus changes shape = no longer functional
Why do smaller organisms have a higher metabolic rate
They have a higher surface area to volume ratio
So will lose MORE heat
So need more metabolic reactions to release heat more
Problem if smaller organism is too cold
Not enough kinetic energy for substrate/enzyme for enzyme catalyses reactions (for E-S complexes to form)
Because not enough heat is released if the metabolic rate is too low
Why do smaller organisms have higher feeding rates than larger organisms?
For enough substrate because they have high metabolic rates to maintain a high enough temperature for E-S complexes to form
To overcome excessive cooling effect due to high SA: vol ratio
