surface area to volume ratio

Question 1

Do smaller or larger organisms have a higher SA:V ratio?

Answer 1

Smaller organisms

Question 2

Relationship between SA:V ratio and metabolic rate [3]

Answer 2

• Increased SA:V ratio = Increased rate of heat loss
• Higher metabolic rate / faster respiration needed
• To generate enough heat to maintain a constant body temperature

Question 3

What adaptations to facilitate exchange do larger organisms have?

Answer 3

specialised surface / organ for gaseous exchange

Question 4

Why do larger organisms need a specialised surface / organ for gas exchange? [4]

Answer 4

• They have a smaller SA:V ratio
• Meaning they have a long diffusion pathway
• Diffusion wouldn’t be fast enough to reach all of the organism’s cells
• As they have a high demand for oxygen and to remove carbon dioxide

Question 5

What other feature of larger organisms means that they need a specialised exchange surface / organ?

Answer 5

Skin is waterproof + gas tight