3.3 SA:V, Gas exchange

Question 1

what can surface area to volume ratio (SA:V) effect?

Answer 1

The rate at which substances diffuse across an organism’s outer surface

Question 2

how does high SA:V affect the rate of diffusion?

Answer 2

These organisms have a large surface area relative to their volume so the diffusion of substances is fast

Question 3

how does low SA:V affect the rate of diffusion?

Answer 3

These organisms have a small surface area relative to their volume so the diffusion of substances is slower

Question 4

what size organisms have a relatively low SA:V?

Answer 4

Larger organisms

Question 5

what size organisms have a relatively high SA:V?

Answer 5

smaller organisms

Question 6

how do substances enter cells in a single celled organism?

Answer 6

they can diffuse directly across the cell membrane

Question 7

explain the diffusion rate in single celled organisms?

Answer 7

quick diffusion rate because the substance only has to travel a small distance

Question 8

why can’t substances simply diffuse into cells in multicellular organisms?

Answer 8

• cells are not in direct contact to external environment
• large diffusion distances between cells and their environment
• Larger organisms have higher metabolic rates, so they need more oxygen and glucose

Question 9

what are 4 key features of specialised exchange surfaces

Answer 9

A large surface area - This provides a larger area across which substances can be exchanged
Thin walls - These minimise the diffusion distance
An extensive blood supply and/or ventilation - This maintains steep concentration gradients
Being surrounded by selectively permeable plasma membranes - This controls what substances are exchanged