Diffusion

Question 1

Substances diffuse though the lipid bilayer at different speeds

Answer 1

• CO2 and O2 + steroid hormones pass through v. quickly
• others pass through more slowly
• due phospholipid bilayer

Question 2

Diffusion

Answer 2

• the net, random movement of particles from a high concentration to a low concentration
• occurs in living and non-living systems where there is a concentration gradient

Question 3

When a uniform concentration is reached

Answer 3

Dynamic equilibrium is established ; no net movement (no diffusion)

Question 4

Rate of diffusion across an exchange surface

Answer 4

• directly proportional to area of the surface
• directly proportional to the concentration
• inversely promotional to distance (length of diffusion pathway)

Question 5

Fick’s Law

Answer 5

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

• applies to situations where there is no barrier to the movement of substances; passive (simple diffusion)
• speed of diffusion is affected by permeability and nature of the membrane and the size and type of particle (properties; charge)

Question 6

Adaptations to increase rate of diffusion

Answer 6

• steep concentration gradient
• high surface area: volume ratio
• minimising distance

Question 7

Facilitated diffusion

Answer 7

• necessary for molecules that are not soluble in lipids
• e.g. glucose, nucleic acids, amino acids, proteins
• passive process down a concentration gradient
• needs channel proteins (may have hydrophilic channels that function as pores along which solutes can pass through