3.1.1a/b Diffusion & Exchange Surfaces

Question 1

What is diffusion

Answer 1

The net random movement of particles from an area of higher concentration to lower concentration, down a concentration gradient, (until an equilibrium is reached)

Question 2

Why is diffusion usually enough to satisfy the needs of a single-celled organism

Answer 2

• Metabolic activity is usually low
• Diffusion distante is short
• SA:V is high due to small size

Question 3

Surface area of a sphere

Answer 3

4πr²

Question 4

Volume of a sphere

Answer 4

4/3 πr^3

Question 5

Relationship between size of organism and its SA:V

Answer 5

As the size of the organism increases, the SA:V decreases

Question 6

2 factors for organisms with a small SA:V

Answer 6

• diffusion distance is too great
• rate of exchange is not fast enough & quantities exchanged are not large enough to meet metabolic demands

Question 7

4 features that effective exchange surfaces have in common

Answer 7

• Increased SA
• Thin layers
• Good blood supply
• Ventilation to maintain

Question 8

Why does increased SA make exchange surfaces more effective

Answer 8

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

Eg includes root hair cells in plants & the villi in the small intestine of mammals

Question 9

Why do thin layers make exchange surfaces more effective

Answer 9

These mean the distance that substances have to diffuse are short, making the process fast & efficient.

Eg includes the alveoli in the lungs & the villi of the small intestine

Question 10

Why does good blood supply make exchange surfaces more effective

Answer 10

The steeper the concentration gradient, the faster diffusion takes place. Having a good blood supply ensures substances are constantly delivered to & removed from the exchange surface. This maintains a steep concentration gradient for diffusion.

Eg the alveoli of the lungs, gills go a fish & the villi of the small intestine

Question 11

Why does ventilation to maintain diffusion gradient make exchange surfaces more effective

Answer 11

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

Eg the alveoli & gills of a fish where ventilation means a flow of water carrying dissolved gases

Question 12

How to calculate SA of cube

Answer 12

1. find area of one side
2. multiply the area of one side by 6 (6 faces)

if all faces are not of equal area, calculate the area of all individual faces and add them up

Question 13

How to calculate V of cube

Answer 13

length x width x height