Exchange Surfaces

Question 1

Explain diffusion

Answer 1

Diffusion is the net random movement of particles from an area of higher concentration to an area of lower concentration down a concentration until an equilibrium is reached.

Question 2

Why may diffusion alone be usually enough to satisfy the needs of single celled organisms.

Answer 2

This is due to single celled organisms low metabolic activity / short diffusion pathway / SA:V ratio is high

Question 3

Explain how increased surface area supports gas exchange and provide examples

Answer 3

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

Examples include root hair cells in plants and the vili in the small intestine of mammals.

Question 4

Explain how thin layers supports gas exchange and provide examples

Answer 4

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

Examples include the alveoli in the lungs and the villi of the small intestine.

Question 5

Explain how good blood supply supports gas exchange and provide examples

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 steep concentration gradient for diffusion.

For example the alveoli fo the lungs, the gills for fish and the vili of the small intestine.

Question 6

Explain how does ventilation work to maintain the diffusion gradient to supports gas exchange and provide examples

Answer 6

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

For example the alveoli and the gills for a fish where ventilation means a flow of water carrying dissolved gases.