surface area to volume ratio

Question 1

what SA:V ratio do smaller animals have?

Answer 1

large

Question 2

what SA:V ratio do larger animals have?

Answer 2

small

Question 3

what is the exchange surface in animals?

Answer 3

lungs

Question 4

what is the exchange surface in single celled organisms?

Answer 4

cell membrane

Question 5

why is diffusion rate quick in single-celled organisms? (2)

Answer 5

● due to small distances substances have to travel

● directly in / out of the cell across cell-surface membrane

Question 6

how may a large animal adapt to compensate for its small SA:V ratio? (2)

Answer 6

● changes that increase surface area

● e.g. folding

Question 7

why do multicellular organisms need specialised exchange organs? (4)

Answer 7

● diffusion across membrane is too slow

● large distance between cells deep within body and outside environment

● larger animals have lower SA:V ratios - difficult to supply large volume of animal

● so multicellular organisms need specialised exchange organs (like lungs)

Question 8

how does body size affect heat exchange? (5)

Answer 8

● rate of heat loss depends on surface area

● large animals - large volume so small surface area (small SA:V)

● makes it harder for it to lose heat from its body

● small animals - small volume so large surface area
(high SA:V)

● so heat is lost more easily

Question 9

outline why smaller organisms need a high metabolic rate (5)

Answer 9

● small animals have higher SA:V ratio

● so loses heat at a higher rate

● higher rate of respiration replaces heat loss (as respiration is exothermic)

● respiration is a metabolic reaction

● so need high metabolic rate to generate enough heat to stay warm

Question 10

how does shape affect heat exchange? (4)

Answer 10

● compact animals - small surface area relative to volume

● minimising heat loss

● less compact animals - larger surface area relative to volume

● increasing heat loss

Question 11

explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake (2)

Answer 11

● larger animals have smaller surface area : volume ratios

● faster diffusion / short diffusion pathway

Question 12

explain why oxygen uptake is a measure of metabolic rate in organisms (1)

Answer 12

oxygen used in respiration, which is a metabolic process