[Unit 4.2] | Diffusion

Question 1

What does “passive” transport mean?

Answer 1

Energy comes from the natural motion of particles, not an external source like ATP.

Question 2

Define diffusion.

Answer 2

Movement of particles across a membrane, following a concentration gradient (high -> low) until the distribution of particles is equal.

Question 3

What is facilitated diffusion?

Answer 3

• A passive process relying on the kinetic motion of diffusing molecules.
• It allows charged/large molecules to travel across the membrane when they otherwise would be unable to (via protein channels/carriers).

Question 4

Explain how diffusion occurs via a protein channel.

Answer 4

If a specific water-soluble ion (charged particle) is present, the channel opens and the ion can pass through the water-filled hydrophillic tube. (High-Low Conc)

Question 5

Explain how diffusion occurs via a protein carrier.

Answer 5

• When a specific large molecule (like glucose) is present, it binds to the carrier.
• the carrier changes shape and deposits the molecule inside the membrane. (High - Low Conc)

Question 6

What 3 factors can impact the speed of diffusion?

Answer 6

• The pathway / distance of diffusion.
• The difference of concentration on either side of the membrane.
• The surface area of the membrane.

Question 7

What is the equation of Fick’s Law?

Answer 7

Rate of Diffusion = (Surface Area * Difference in Conc) / Length of Diffusion Pathway