Surface area to volume ratio

Question 1

What happens as organisms increase in size?

Answer 1

• Surface area increases
• Vol increases
• SA:Vol ratio decreases

Question 2

Why does SA:Vol ratio decrease as organisms get bigger?

Answer 2

Since whilst SA increases in 2 dimensions (squared), vol increases in 3 dimensions (cubed)

Therefore vol increases at quicker rate than SA

Question 3

What is a small organisms (e.g. bacterium) SA:Vol ratio?

Answer 3

Very high - due to this diffusion is efficient for gas + substance exchange

Question 4

What is a large organism’s (e.g. elephant) SA:Vol ratio?

Answer 4

Very low

Question 5

What do organisms need to do as they get bigger?

Answer 5

They need to develop specialised exchange surfaces

Question 6

What are the specialised exchange surfaces that large organisms have?

Answer 6

• Folding + branching to increase SA
• Very thin, reduces diffusion distance
• Well supplied with blood vessels, maintains high conc gradient
• Ventilation of gases or water, maintains high conc gradient

Question 7

How can you overcome the limitations of diffusion?

Answer 7

Have presence of transport system so substances can be quickly moved between cells