7.1 Specialised exchange surfaces

Question 1

why is diffusion alone is enough to support the needs of single-celled organisms

Answer 1

• metabolic activity is relatively low so O2 and CO2 demands are low
• SA:V ratio is large

Question 2

why is diffusion not enough for larger organisms

Answer 2

• made up of many cells arranged in tissues, organs and organ systems
• metabolic activity is higher
• distance between cells where oxygen is needed and the supply of oxygen is too far
• the bigger the organism, the smaller the SA:V ratio

Question 3

equation for surface area of a sphere

Answer 3

4 x pi x r^2

Question 4

equation for volume of a sphere

Answer 4

4/3 x pi x r^3

Question 5

what are characteristic features of efficient exchange surfaces

Answer 5

• increased surface area (overcomes limitations of SA:V ratio)
• thin layers (diffusion distances are shorter so its faster)
• good blood supply (substances constantly delivered and removed to maintain steep concentration gradient)
• ventilation to maintain diffusion gradient (maintain concentration gradients)