3.3.1 - surface area to volume ratio Flashcards
what is an object’s surface area to volume ratio?
a way of describing how close every internal part of it is to it’s surface
what is the SA:V ratio of small objects like?
they have a high SA:V ratio meaning every part of the object is close to the edge - things can move in and out quickly across the short distance
what is the SA:V ratio of large objects like?
they have a low SA:V ratio so some parts of the object are a long way from the edge - things take longer to get in and out due to the long distance from the edge to the middle
what is the relationship between the size of an organism and SA:V ratio?
the larger an organism gets, the lower its SA:V ratio becomes
what is the relationship between the mass of an organism and metabolic rate?
the greater the mass of an organism, the higher its metabolic rate (amount of energy expended in a time period), because it requires more efficient delivery of oxygen to cells as more respiration is needed
why have multicellular organisms evolved complex mass transport and exchange systems?
because they need efficient delivery of oxygen and nutrients to cells - the rate of exchange of these substances depends on surface area in contact with the surroundings, and larger organisms have smaller SA:V ratios, so it is harder to get oxygen and nutrients from the environment
what are the advantages and disadvantages of unicellular organisms having a high SA:V ratio?
adv - SA large enough to absorb substances required, diffusion from environment is fast due to short diffusion distance, all of cell has surface exposed to outside so can exchange materials directly with environment
dis adv - lose heat energy and water quickly
what are the advantages and disadvantages of multicellular organisms having a low SA:V ratio?
adv - lose less heat energy
dis adv - can’t absorb enough substances to supply their large volume, large diffusion distance means diffusion through outer surface is too slow to supply cells efficiently, internal mass transport systems required as some cells have no surfaces exposed to outside
how can an animal’s shape control its temperature?
increasing SA:V ratio increases heat loss
large organisms with low SA:V ratios may have large ears to increase their surface area in warm environments
animals in cold environments are streamlined with compact body shapes to give a smaller SA:V ratio
how might the development of systems in larger organisms that live in warm environments change due to their high SA:V ratio?
they may have kidney structure adaptations so they produce less urine to compensate for water lost through evaporation
