7.1 Specialised Exchange Surfaces

Question 1

Why isn’t diffusion alone enough to supply the needs of single-felled organisms?

Answer 1

The metabolic activity of a singled-called organism is usually low, so the oxygen de,ands and carbon dioxide production of the cell are relatively low
The surface area to volume ratio of the organism is relatively large

Question 2

What are the characteristics of effective exchange surfaces?

Answer 2

• increased surface area
• thin layers
• good blood supply
• ventilation to maintain diffusion gradient

Question 3

How does an increased surface area make an exchange surface area effective?

Answer 3

It provides the area needed for exchange and overcomes the limitations of SA:V ratio in larger organisms
E.g. root hair cells in plants
Villi in the small intestine

Question 4

How do thin layers make an exchange surface area effective?

Answer 4

It makes the diffusion distance shorter, making the process fast and efficient
E.g. alveoli in lungs
Vikki of the small intestine

Question 5

How does a good blood supply make an exchange surface area effective?

Answer 5

• The steeper the concentration gradient, the faster diffusion takes place
• Having a good blood supply ensures substances are constantly delivered to and removed from the exchange surface
• This maintains a step concentration gradient for diffusion
  E.g. alveoli of the lungs gills of a fish, villi if the small intestine

Question 6

How does ventilation to maintain diffusion gradient make an exchange surface area effective?

Answer 6

• helps maintain concentration gradients and make the process more efficient
  E.g. alveoli and the gills of a fish