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.

Question 7

Why do microscopic organisms exchange all substances it needs directly through the cell membrane

Answer 7

Has a relatively low rate of respiration (not very active organisms)

The surface area of the cell membrane of the amoeba is relatively large ,compared to the volume of the cell.

Question 8

How to calculate surface area to volume ration

Answer 8

Surface area to volume ration=

Surface area

———————

Volume

Question 9

What is the trend with SA:V as organism get larger

Answer 9

As organisms get larger the surface area to volume ratio decreases

Question 10

What systems do multicellular organisms have to combat the small SA:V

Answer 10

Specialised gas exchange surface with a large SA

Specialised transport systems in order to carry molecules around the body