topic 3.1 Surface area to volume ratio

Question 1

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

Answer 1

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

Question 2

How is SA:V calculated? Use an example

Answer 2

Divide surface area (size length x side width x number of sides) by volume (length x width x depth)

Question 3

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

Answer 3

Easier to find + more accurate because irregular shapes

Question 4

What is metabolic rate? Suggest how it can be measured

Answer 4

● 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 5

Explain the relationship between SA:V and metabolic rate

Answer 5

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 6

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

Answer 6

1. Changes to body shape (eg. long / thin)
   ○ Increases SA:V and overcomes (reduces) long diffusion distance / pathway
2. 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