5.3 - Diffusion

Question 1

Define passive transport

Answer 1

A passive (non-energy requiring) energy process and doesn’t use energy from cellular respiration, uses energy from natural motion of the cell.

Question 2

Define equilibrium

Answer 2

Balance/no difference in concentration

Question 3

Define diffusion

Answer 3

Net movement of particles from a region of higher concentration to a region of lower concentration DOWN the concentration gradient.

It is a passive process

Question 4

What happens to the rate of diffusion as distance increases?

Answer 4

As distance increases, rate of diffusion decreases

- At high speeds particles are colliding more and more so they lose their energy over long distances.

Question 5

What factors affect rate of diffusion?

Answer 5

Temperature
- Higher temp, more kinetic energy, faster particle movement

Concentration gradient (difference)
- Overall movement is greater from high conc. to low

Question 6

What is simple diffusion?

Answer 6

Diffusion in the absence of a barrier or membrane

Question 7

What happens during diffusion across a membrane?

Answer 7

• Must cross phospholipid bilayer
• Non-polar molecules (e.g. O2) diffuse freely down concentration gradient
• Hydrophobic interior of bilayer repels ions (due to charge) and polar molecules pass slowly
• Small polar molecules pass easier than large ones

THUS MAKING MEMBRANES PARTIALLY PERMEABLE?

Question 8

What factors affect the rate of membrane diffusion?

Answer 8

Surface area: Larger SA of exchange surface = greater R.o.D

Membrane thickness - thinner membrane = greater R.o.D

Question 9

Define facilliated diffusion

Answer 9

Diffusion across a membrane whereby polar molecules & ions travel through a channel/carrier protein

(down conc. gradient, no energy requires)

Membranes with protein channels are SELECTIVELY PERMEABLE

Question 10

What factors affect the rate of facilitated diffusion?

Answer 10

• Temp
• Membrane thickness
• Surface area
• No. of channel/carrier proteins

Question 11

What is dialysis tubing?

Answer 11

• has pores the size on membranes

- is partially permeable (water passes through, larger starch molecules cannot)

Question 12

How do you set up a model cell using dialysis tubing?

Answer 12

1) Tie one end of tube, add solution and tie the other end.

Question 13

How do you investigate diffusion across membranes?

Answer 13

1) Place model cell in another solution (with different sized molecules or conc.)
2) Calculate R.o.D (or osmosis) by measure cell mass change or Benedicts test to assess glucose conc.