Mod. 3 exchange surfaces and breathing

Question 1

How do single celled organisms exchange metabolic molecules with their external environment?

Answer 1

diffusion. Their metabolic activity is low and their SA:V ratio is large.

Question 2

Why can larger organisms not use diffusion alone for gas exchange?

Answer 2

Their SA:V ratio is too small and their metabolic rate is too high, so diffusion from the surface only would not meet the metabolic demands from the cells.

Question 3

What are the common traits of specialised exchange surfaces?

Answer 3

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

Question 4

How does an increased surface area affect a specialised exchange surface?

Answer 4

increases surface through which diffusion can happen, overcoming the limitations of the small SA:V ratio.

Question 5

How do thin layers affect specialised exchange surfaces?

Answer 5

The distances the molecules have to diffuse are shorter, and therefore more efficient, the process is then faster.

Question 6

How does a good blood supply affect a specialised exchange surface?

Answer 6

Increases and maintains a steep concentration gradient across which molecules can diffuse. The steeper the gradient the faster the diffusion.