7.1 Specialised Exchange Surfaces

Question 1

What are the two main reasons as to why diffusion is enough to supply the needs of single-celled organisms?

Answer 1

-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 of the organism is large

Question 2

What happens to the surface area to volume ratio as the size of an organism increase?

Answer 2

The SA:V ratio decreases

Question 3

What have large multicellular organisms evolved for the exchange of substances?

Answer 3

Specialised systems, and exchange surfaces

Question 4

What are the key features of specialised exchange surfaces?

Answer 4

Increased surface area, thin layers, good blood supply, ventilation to maintain diffusion gradient

Question 5

How does an increased surface area help an exchange surface?

Answer 5

Provides the area needed for exchange, and overcomes the limitations of the surface area : volume ratio of larger organisms.

Question 6

How do thin layers help an exchange surface?

Answer 6

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

Question 7

How does a good blood supply help an exchange surface?

Answer 7

-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.

Question 8

How does having ventilation to maintain a diffusion gradient help an exchange surface?

Answer 8

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