Surface Area: Volume Ratio

Question 1

Why is a large surface area required for the exchange of substances?

Answer 1

For efficient exchange to occur, a large surface area is needed since the exchange takes place over the surface.

Question 2

Describe the surface area: volume ratio of single celled organisms?

Answer 2

Large SA:V ratio so exchange can occur over the outer surface

Question 3

Why don’t larger multicellular organisms exchange over their body surface?

Answer 3

• the larger the organism the smaller the SA:V ratio
• need for waterproofing (if living on land)
• diffusion is much to slow (ficks law)

Question 4

What is the solution for SA:V ratio getting smaller as the organism gets bigger?

Answer 4

Have specialised exchange surfaces with very large SAs eg. Lungs, Gills, Tracheal system

Question 5

What is the solution for the need to waterproofing terrestrial organisms?

Answer 5

Have specialised exchange surfaces that are tucked away within the body to reduce water loss. This means the outer skin can become waterproof.

Question 6

What is the solution to the problem that diffusion is too slow over long distances?

Answer 6

A transport system, a system of open tubes to carry air to every cell

Question 7

What are the features of a specialised exchange surface?

Answer 7

• large surface area
• very thin (short diffusion distance)
• maintains a diffusion gradient
• selectively permeable

Question 8

What’s the relationship with metabolic rate and SA:V ratio?

Answer 8

The greater the metabolic rate, the greater the quantities of the substances that need to be exchanged. Therefore they require an exchange surface with a larger surface area and a transport system to meet the requirements of the organism.