Specialised exchange surfaces 7.1

Question 1

what 2 reasons are there for diffusion alone being enough to supply the needs of a single-celled organism

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 ration of the organism is large

Question 2

what are some reasons why diffusion alone cannot be used to supply the needs of multicellular organisms

Answer 2

The amount of energy used for things such as moving means the oxygen demands of the muscle cell deep in the body will be high and they will produce lots of carbon dioxide. The distance between the cells where the oxygen is needed and the supply of oxygen is too far for effective diffusion to take place.

The bigger the organism, the smaller the SA:V ratio. so gases can’t be exchanged fast enough or in large enough amounts for the organism to survive

Question 3

what are the characteristics shared by all 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 help substance exchange

Answer 4

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 villi in the small intestine of mammals

Question 5

How do thin layers help substance exchange

Answer 5

These mean the distance 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 6

How does good blood supply help substance exchange

Answer 6

The steeper the concentration gradient, the faster diffusion takes place.
Having a good blood supply ensures substances are constantly delivered to and remove from the exchange surface.
This maintains a steep concentration gradient for diffusion. For example the alveoli of the lungs, the gills of a fish and the villi of the small intestine

Question 7

How does ventilation to maintain diffusion gradient help substance exchange

Answer 7

For gases, a ventilation system also helps maintain concentration gradients and makes the process more efficient, for example the alveoli and the gills of a fish where ventilation means a flow of water carrying dissolved gases