3.1 Surface area to volume ratio

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

• as size increases, sa:v tends to decrease

• more thin / flat / folded / elongated structures increase sa:v

Suggest an advantage of using sa:mass for organisms instaed of sa:v

easier / quicker to find / more accurate because irregular shapes

What is metabolic rate? Suggest how it can be measured

• 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

Explain the relationship between sa:v and metabolic rate

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 i.e. replace lost heat

Explain the adaptations that facilitate exchange as sa:v reduces in large organisms

1. changes to body shape e.g. long or thin

   • increases sa:v and overcomes long diffusion distance / pathway

2. development of systems, such as a specialised surface / organ for gaseous exchange

   • increases internal sa:v and overcomes long diffusion distance / pathway

   • maintain a concentration gradient for diffusion e.g. by ventilation / good blood supply