3.1 Organisms exchange substances with their environment

Question 1

what are two ways in which exchange can tale place?

Answer 1

1. passively
2. actively

Question 2

name two features organisms have evolved to enable exchange of substances

Answer 2

1. flattened shapes so no cell is ever far from the surface
2. specialised exchange surfaces with large areas to increase surface are to volume ratio

Question 3

how is the diffusion gradient of O2 and CO2 in and out of cells maintained? [2]

Answer 3

mitochondria have the lowest O2 concentration in cells due to respiration, and the highest concentration of CO2. this maintains the diffusion gradient in and out of the cells as O2 will diffuse into the cell down the concentration gradient to an area of lower concentration.

Question 4

how does the surface area to volume ratio of organisms change as the size of the organism increases?

Answer 4

it decreases

Question 5

name five features of specialised exchange surfaces

Answer 5

1. high SA:V ratio to increase rate of diffusion
2. very thin so diffusion distance is short so materials cross exchange surface rapidly
3. selectively permeable membrane to allow selected materials to cross
4. movement of environmental medium to maintain diffusion gradient
5. transport system to ensure movement of internal medium to maintain diffusion gradient

Question 6

how can the relationship between exchange factors be expressed as an equation?

Answer 6

diffusion ∝ (surface area x difference in concentration) / length of diffusion path