7.1 Specialised Exchange Surfaces

Question 1

What is an amoeba?

Answer 1

What is an amoeba?

Question 2

Why don’t amoeba need specialised exchange surfaces?

Answer 2

All the oxygen needed + waste CO2 produced can be exchanged with the external env. by diffusion through the cell surface.
The distances substances have to travel are very small.

Question 3

What are the 2 reasons why diffusion alone is enough to supply the needs of single-celled organisms?

Answer 3

1. Low metabolic activity, so O2 demands + CO2 production of the cell are low
2. Large SA:V ratio

Question 4

Why do large organisms needs effective exchange surfaces?

Answer 4

• Higher metabolic demands than amoeba
• Distance between oxygen-demanding cells and oxygen supply is too far for effective diffusion
• Bigger organisms have smaller SA:V ratio - gases can’t be exchanged fast enough for organisms to survive

Question 5

What is the equation to calculate the volume of a sphere?

Answer 5

3/4πR3

Question 6

What are the 4 common characteristics of effective exchange surfaces?

Answer 6

1. Increased SA
2. Thin layers
3. Good blood supply
4. Ventilation to maintain diffusion gradient

Question 7

How does increased surface area provide effective exchange surfaces?

Answer 7

Larger SA provides the area needed for exchange and overcomes the limitations of the SA:V ratio of larger organisms.

Example: Root hair cells
Villi in small intestine of mammals

Question 8

How do thin layers provide effective exchange surfaces?

Answer 8

Thin layers mean distances substances have to diffuse are short, making the process fast and efficient.

Example:
Alveoli in lungs
Villi in small intestine

Question 9

How does a good blood supply provide effective exchange surfaces?

Answer 9

The steeper the concentration gradient, the faster diffusion occurs.

A good blood supply ensures substances are constantly delivered to + removed from exchange surfaces.
This maintains a steep concentration gradient for diffusion.

Example:
Alveoli in lungs
Gills of fish
Villi of small intestine

Question 10

How does ventilation to maintain diffusion gradient provide effective exchange surfaces?

Answer 10

For gases, a ventilation system helps maintain concentration gradients + makes the process more efficient.

Example:
Gills of fish, where ventilation means a flow of water carrying dissolved gases