3.1 - Surface area to volume ratio

Question 1

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

Answer 1

• Large(r) organisms have a small(er) surface area:volume (ratio)
  / Small(er) organisms have a large(r) surface area:volume (ratio)
• Overcomes long diffusion pathway
  / Faster diffusion

Question 2

Mammals such as a mouse and a horse are able to maintain a constant body temperature. Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse. (3)

Answer 2

• (Smaller so) larger surface area to volume ratio
• More/faster heat loss (per gram/in relation to body size)
• (Faster rate of) respiration/ metabolism releases heat
  ‘accept respiration/metabolism replaces heat’

Question 3

Describe the relationship between size and surface area to volume ratio of organisms. (1)

Answer 3

• As size increases, ratio (of surface area to volume) decreases

Question 4

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

Answer 4

• (Oxygen used in) respiration, which provides energy / ATP
• (Oxygen is used in) respiration, which is a metabolic process / chemical reaction