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 ratio tends to decrease
• more thin / flat / folded / elongated / structures increase SA:V

Question 2

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

Answer 2

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

Question 3

What is metabolic rate? Suggest how it can be measured

Answer 3

• 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 4

Explain the relationship between SA:V and metabolic rate

Answer 4

• as SA:V increases (smaller organisms), metabolic rates 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 I.e. replace lost heat

Question 5

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

Answer 5

1. Change to body shape (e.g. long / thin)
   - increases SA:V ratio and overcomes (reduces) long diffusion distance / pathway
2. Development of systems, such as specialised surface / organ for gaseous exchange e.g. lungs
   - increase (internal) SA:V and overcomes (reduces) long diffusion distance / pathway
   - maintain a concentration gradient for diffusion e.g. by ventilation / good blood supply