Surface area to volume ratio

Question 1

What is the relationship between the size & structure of an organism and its SA:V ratio?

Answer 1

• as size increases SA:V decreases
• thin/flat/folded/elongated structures increase SA:V

Question 2

How is SA:V calculated?

Answer 2

• divide surface area (l x w x no. of sides) by volume (l x w x h)

Question 3

What is an advantage of calculating SA: mass for organisms instead of SA:V?

Answer 3

• easier/ quicker to find
• more accurate because of irregular shapes

Question 4

What is metabolic rate?

Answer 4

• metabolic rate = amount of energy used up by an organism within a given time period
• often measured by oxygen uptake since it’s used in aerobic respiration to make ATP for energy release

Question 5

What is the relationship between SA:V and metabolic rate?

Answer 5

as SA:V increases metabolic rate in smaller organisms increases as:
- rate of heat loss per unit body mass increases
- so organisms need higher rate of respiration
- to release enough heat to maintain constant body temp

Question 6

What adaptations facilitate exchange as SA:V reduces in larger organisms?

Answer 6

• changes in body shape (long/thin) which increases SA:V & overcomes long diffusion distance
• development of systems like specialised surface for gas exchange (lungs) which increases internal SA:V & overcomes long diffusion distance and maintains a conc gradient for diffusion (good blood supply)