Specialised Exchange Surfaces

Question 1

SA/V Ratio

Answer 1

Ratio = Surface Area / Volume

The larger the SA : V ratio the easier it is for the organism to diffuse oxygen from the supply to the cells. The bigger the organism the smaller the SA : V ratio so gases cannot be exchanged fast enough or in the right amounts for the organism to survive.

Question 2

Why is diffusion alone enough to supply the needs of single celled organisms ?

Answer 2

• the metabolic activity of a single-celled organism is usually low, so the oxygen demands and carbon dioxide production of the cell are relatively low.
• the surface area to volume ratio on the organism is large

Question 3

Characteristic features of Specialised Exchange Surfaces

Answer 3

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

Question 4

EXPLAIN: Increased Surface Area

Answer 4

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

Example: root hair cells in plants and villi in the small intestines

Question 5

EXPLAIN: Thin Layers

Answer 5

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

Example: alveoli in the lungs, or villi of the small intestine

Question 6

EXPLAIN: Good Blood Supply

Answer 6

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.

Example: alveoli, gills of a fish or villi

Question 7

EXPLAIN: Ventilation to Maintain Diffusion Gradient

Answer 7

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

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