Simple and facilitated diffusion

Question 1

What is diffusion?

Answer 1

Diffusion is the net movement of particles from an area of high concentration to an area of low concentration down the concentration gradient

Question 2

Is diffusion an active or a passive process?

Answer 2

Passive as it does not requires energy

Question 3

What are the two types of diffusion?

Answer 3

• Simple
• Facilitated

Question 4

What is simple diffusion?

Answer 4

The diffusion of small and non-polar molecules across cell membranes

Question 5

What are some molecules that can pass through the cell membrane via simple diffusion?

Answer 5

• Oxygen
• Carbon dioxide

Question 6

Only some molecules can pass through the cell membrane via simple diffusion. Why is this?

Answer 6

The molecule must be small so that it can pass through the spaces between phospholipids
The molecule must also be non-polar so that they can dissolve in the centre of the membrane

Question 7

What is facilitated diffusion?

Answer 7

The diffusion of large and polar molecules across cell membranes

Question 8

What two types of proteins are involved in facilitated diffusion?

Answer 8

• Carrier proteins
• Channel proteins

Question 9

What is the role of carrier proteins?

Answer 9

To transport large molecules across cell membranes

Question 10

How does a carrier protein transport molecules across a cell membrane?

Answer 10

1) A large molecule attaches to a carrier protein
2) This causes the carrier protein to change shape
3) The carrier protein releases the molecule on the opposite side of the membrane

Question 11

What is the role of channel proteins?

Answer 11

To transport ions across cell membrane

Question 12

How does a channel protein transport molecules across a cell membrane?

Answer 12

Forms pores in the cell membrane for ions to diffuse through

Question 13

What are the factors that affect the rate of diffusion?

Answer 13

• Temperature
• Concentration gradient
• Thickness of membrane
• Surface area
• Number of carrier or channel proteins

Question 14

How does temperature affect the rate of diffusion?

Answer 14

At higher temps, particles have more kinetic energy and diffuse faster

Question 15

How does the concentration gradient affect the rate of diffusion?

Answer 15

The higher the concentration gradient, the faster the rate of diffusion

Question 16

How does the thickness of the membrane affect the rate of diffusion?

Answer 16

Particles travel less distance in thinner exchange surfaces so they will diffuse faster

Question 17

How does the surface area affect the rate of diffusion?

Answer 17

A larger the surface area mean more particles can cross the membrane at once, so faster diffusion

Question 18

How does the number of carrier and channel proteins affect the rate of diffusion in facilitated diffusion?

Answer 18

The more carrier and channel proteins there are, the faster the rate of diffusion

Question 19

In facilitated diffusion, the rate of diffusion will increase as concentration increases however will eventually plateau while concentration is still increasing. Why is this?

Answer 19

All of the carrier and channel proteins are saturated and cannot work any faster
- They are limiting factors