Surface Area to Volume Ratio

Question 1

The larger the organisms size is
What is the surface area to volume ratio

Answer 1

Smaller

Question 2

What is the surface area of a cube that is 3 by 3 by 3 cm

Answer 2

SA= 3x3=9cm x 6= 54cm2
V= 3x3x3=27cm3
SA:V=54:27= 2:1

Question 3

Describe the relationship between the size and structure of an organism and
its surface area to volume ratio (SA:V)

Answer 3

● As size increases, SA:V tends to decrease
● More thin / flat / folded / elongated structures increase SA:V

Question 4

Suggest an advantage of calculating SA:mass for organisms instead of SA:V

Answer 4

Easier / quicker to find / more accurate because irregular shapes

Question 5

What is metabolic rate? Suggest how it can be measured

Answer 5

● Metabolic rate = amount of energy used up by an organism within a given period of time
● Often measured by oxygen uptake → as used in aerobic respiration to make ATP for energy release

Question 6

Explain the relationship between SA:V and metabolic rate

Answer 6

As SA:V increases (smaller organisms), metabolic rate increases because:
● Rate of heat loss per unit body mass increases
● So organisms need a higher rate of respiration
● To release enough heat to maintain a constant body temperature ie. replace lost heat

Question 7

Explain the adaptations that facilitate exchange as SA:V reduces in larger
organisms

Answer 7

Changes to body shape (eg. long / thin)
○ Increases SA:V and reduces long diffusion distance / pathway
Development of systems, such as a specialised surface / organ for gaseous exchange e.g. lungs:
○ Increases (internal) SA:V and overcomes (reduces) long diffusion distance / pathway
○ Maintain a concentration gradient for diffusion eg. by ventilation / good blood supply