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:

Answer 1

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

Question 2

How is SA:V calculated?

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 / quicker to find / more accurate because irregular shapes.

Question 4

What is metabolic rate? Suggest how it can be measured:

Answer 4

1. Metabolic rate = amount of energy used up by an organism within a given period of time.
2. 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

1. As SA:V increases (smaller organisms), metabolic rate increases because:
2. Rate of heat loss per unit body mass increases
3. So organisms need a higher rate of respiration
4. 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