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

Why is diffusion a passive process?

Answer 2

Diffusion is a passive process. This means that the molecule will continue to move down their conc gradient WITHOUT USING ENERGY from the cell.

Question 3

Why does diffusion occur?

Answer 3

In a gas or liquid the molecules or ions move around because of the kinetic energy that they possess.
They move around at RANDOM colliding with one another.
As they collide they change direction.
The closer they are together the more likely they are to collide with one another.
When they do collide they change direction.
The closer the molecules are the more likely they are to collide with one another.

Question 4

How many types of ways are there for passive transport of materials to occur in?

Answer 4

There are 2 types of ways to passively transport materials:
1. Simple diffusion
Simples diffusion is a passive process and involves the transport of materials across membranes through the lipid bilayer.
2. Facilitated diffusion
Facilitate means ‘to help’
Facilitated diffusion is another type of diffusion in which PROTEINS in the membrane help molecules to diffuse.

Question 5

How do very small molecules diffuse?

Answer 5

Very small molecules- gases such as oxygen and carbon dioxide are able to diffuse through the lipid bilayer as they’re small enough.

Question 6

How do lipid based molecules diffuse?

Answer 6

Lipid based molecules. As the membrane is made of phospholipids, fat-soluble molecules can simply pass through the bilayer e.g. Steroid hormones are lipid based and diffuse through membranes.

Question 7

What does the direction of molecules relate to?

Answer 7

The direction of molecules and ions is related to the concentration gradient between the cell exterior and the cell interior.

Question 8

When will diffusion stop?

Answer 8

Diffusion continues until equilibrium is reached i.e. Until there are EQUAL CONCENTRATIONS of molecules or ions on either side of the membrane.

Question 9

What is the following known as:

• when there are equal concentrations of molecules or ions on wither side of the membrane?

Answer 9

Dynamic equilibrium

Question 10

Even when dynamic equilibrium is reached do the molecules continue to move randomly?

Answer 10

• the molecules continue to move randomly and at an EQUAL RATE in both directions across the membrane.

Question 11

What type of molecules would need facilitated diffusion?

Answer 11

• SMALL CHARGED particles such as sodium ions or LARGER molecules such as GLUCOSE cannot pass through the lipid bilayer so must pass through protein molecules.

Question 12

How many types of proteins are involved in facilitated diffusion?

Answer 12

There are 2 types of proteins involved in facilitated diffusion:

• channel proteins (water filled pores)
• carrier proteins (transport proteins)

Question 13

What are channel proteins?

Answer 13

Channel proteins basically form pores in the membrane, which are often shaped to only allow one type of ion through
Many channel proteins are ‘gated’ meaning they can be opened or closed

Question 14

Give an example of a channel protein?

Answer 14

Gated sodium ion channel proteins are involved with the working of the nervous system.

Question 15

What is the purpose of the pores in channel proteins?

Answer 15

Protein ‘pore’ allows water soluble molecules or ions through e.g. Calcium ions

Question 16

What are carrier proteins also known as?

Answer 16

Carrier proteins are also known as transport proteins.

Question 17

What are carrier proteins?

Answer 17

Carrier proteins are shaped so that a specific molecule e.g. Glucose can fit into them at the membrane surface.

THINK OF THE WATER DEMONSTRATION

Question 18

How do carrier proteins work?

Answer 18

When the specific molecule fits/is complementary, the protein changes shape to allow the molecule through to the other side of the membrane

Question 19

Do cells and organelles have the same carrier and channel proteins?

Answer 19

NO

Cells and organelles have different carrier and channel proteinsb

Question 20

Is the rate of diffusion affected by only 1 factor?

Answer 20

No, the rate of diffusion is affected by a number of factors.

Question 21

Describe how an increase in temperature affects the rate of diffusion?

Answer 21

Increasing the temperature gives molecules more kinetic energy therefore increasing collisions. The rate of random movement increases
… and so the rate of diffusion increases.

Question 22

How is the rate of diffusion affected when the temperature is lowered?

Answer 22

Lowering the temperature decreases the random movement of molecules and the rate of transport is reduced.

Question 23

Explain how concentration gradient affects the rate of diffusion?

Answer 23

Having more molecules on one side of a membrane increases the concentration gradient.
This increase the rate of diffusion

Question 24

Explain how surface area affects the rate of diffusion?

Answer 24

Diffusion across membranes occurs more RAPIDLY if there is a GREATER surface area to diffuse across.

Question 25

What shape do red blood cells have in order to increase the surface area for diffusion?

Answer 25

Cells are adapted to increase the surface area for diffusion
E.g. Red blood cells are bi-concave

Question 26

Explain how distance/thickness effect the rate of diffusion?

Answer 26

Diffusion is slowed down by THICK membranes, as there’s a greater distance for molecules to travel.
E.g. Alveolar walls are only 1 cell thick
This creates a short diffusion distance

Question 27

Explain how stirring affects the rate of diffusion?

Answer 27

Stirring a liquid 
or the MOVEMENT OF AIR CURRENTS in a gas
Increases the movement of molecules 
And thus the rate of diffusion 
E.g. Stirring sugar in tea

Question 28

Explain how the size of molecules affects the rate of diffusion?

Answer 28

Smaller molecules or ions diffuse more quickly than larger ones