3.3.1 Surface area to volume ratio ( 3.3 Organisms exchange substances with their environment)

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 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 to find 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 a 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 , 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 temp

Question 6

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

Answer 6

1) changes to body shape
• increases SA:V and overcomes long diffusion pathway
2) Development of systems such as organs for gaseous exchange e.g lungs :
• increases SA:V and overcomes long diffusion pathway
• Maintain a conc gradient for diffusion