Topic 2B - Year 1 - Cell Membranes - 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.

Question 2

At which point will diffusion stop?

Answer 2

Diffusion will stop when particles are evenly distributed through a liquid or a gas.

Question 3

In which direction do particles move when diffusion occurs?

Answer 3

Particles move down the concentration gradient , the move from areas of high concentration to areas of low concentration.

Question 4

Is any energy required for the process of diffusion to occur?

Answer 4

No energy is needed for diffusion to occur , diffusion is a passive process.

Question 5

Name the two types of diffusion

Answer 5

Facilitated diffusion

Simple diffusion

Question 6

Explain simple diffusion

Answer 6

simple diffusion occurs when molecules diffuse directly through the cell membrane (phospholipid bilayer)

Question 7

Which molecules can pass through a cell membrane by simple diffusion and why is this the case?

Answer 7

Oxygen and carbon dioxide can pass through the plasma membrane by simple diffusion , this is the case as oxygen and carbon dioxide molecules are small and hence can pass through between spaces between the phospholipids , carbon dioxide and oxygen are also non polar , hence they are soluble in lipids and can dissolve in the hydrophobic part of the bilayer.

Question 8

Which 3 factors affect the rate of simple diffusion?

Answer 8

The concentration gradient
The thickness of the exchange surface
The surface area

Question 9

How does an increase in the concentration gradient affect the rate of diffusion?

Answer 9

The higher the concentration gradient the greater the rate of diffusion.

Question 10

How does the thickness of the exchange surface affect the rate of diffusion?

Answer 10

As the thickness of the exchange surface decreases the rate of diffusion increases.

Question 11

How does an increase in cell surface area affect the rate of diffusion?

Answer 11

As the surface area increases the rate of diffusion also increases.

Question 12

How is facilitated diffusion different from simple diffusion?

Answer 12

Facilitated diffusion utilises carrier and channel proteins in order to help charged or large particles diffuse across the CSM.

Question 13

In facilitated diffusion in which way do particles move?

Answer 13

In facilitated diffusion particles diffuse down the concentration gradient from areas go high concentration to areas of low concentration.

Question 14

Is facilitated diffusion a passive process?

Answer 14

Facilitated diffusion is a passive process it does not use energy.

Question 15

Name the two types of proteins that can facilitate the diffusion of large or charged particles across a CSM:

Answer 15

Carrier proteins

Channel proteins

Question 16

Which type of molecules do carrier proteins help cross the membrane?

Answer 16

Carrier proteins facilitate the movement or large molecules across the membrane.

Question 17

Is there one generic carrier protein?

Answer 17

No there is not one generic carrier protein , different carrier proteins facilitate the diffusion of different large molecules?

Question 18

Explain how carrier proteins facilitate the movement of large particles:

Answer 18

Firstly the large molecule to be diffused attaches to a carrier protein in the membrane

In response to the the carrier protein changes shape to allow the molecule through.

As the carrier protein changes its shape it releases the large molecule on the opposite site of the membrane.

Question 19

Carrier proteins and channel proteins can be referred to collectively as ?

Answer 19

Transport proteins

Question 20

Which type of molecules do channel proteins facilitate the diffusion of?

Answer 20

Channel proteins facilitate the diffusion of charged particles like ions across the cell membrane down the concentration gradient,

Question 21

Is there just one generic channel protein ?

Answer 21

No there is not one generic channel protein , different channel proteins facilitate the diffusion of different charged particles.

Question 22

Which factors affect the rate of facilitated diffusion?

Answer 22

The concentration gradient

The abundance of carrier and channel proteins

Question 23

How does the concentration gradient affect the rate of facilitated diffusion?

Answer 23

If the concentration gradient is steeper then the rate of diffusion will increase

Question 24

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

Answer 24

If there is a greater abundance of channel and carrier proteins then the rate of facilitated diffusion will be greater. If there are not enough channel or carrier proteins then they become a limiting factor as even as you increase the concentration gradient the rate of diffusion is not increased as the proteins present are all being occupied

Question 25

How do you work out the rate of diffusion?

Answer 25

To work out the rate of diffusion at a certain point in time using a graph you draw a tangent to the graph at the given time and the gradient of this line will dictate the rate of diffusion.