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

-as size increases, SA:V tends to decrease
-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

Answer 4

-the amount of energy used up by an organism within a given period of time

Question 5

how can metabolic rate be measured

Answer 5

-often measured by oxygen uptake → as used in aerobic respiration to make ATP for energy release

Question 6

explain the relationship between SA:V and metabolic rate

Answer 6

-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
-so release enough heat to maintain a constant body temperature ie. replace lost heat

Question 7

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

Answer 7

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