1. Diffusion and Facilitated Diffusion

Question 1

What are the 3 states of matter?

Answer 1

solids, liquids and gases

Question 2

What are solids, liquids and gases made up of?

Answer 2

particles - atoms, ions and molecules

Question 3

Describe the movement of particles in liquids and gases.

Answer 3

continual random* motion

• the direction of movement is random

Question 4

What is the case if there is ‘no net movement’ of particles in a liquid or gas?

Answer 4

they are evenly spread and remain evenly spread despite continually moving

Question 5

What is the case if particles are unevenly spread? What does this cause?

Answer 5

• there is a higher concentration in one region than another

- diffusion

Question 6

Define ‘diffusion’.

Answer 6

the passive movement of particles from a region of higher concentration to a region of lower concentration, as a result of the random motion of particles

Question 7

Why does diffusion occur?

Answer 7

because more particles move from the region of higher concentration to the region of lower concentration than in the opposite direction

Question 8

Can diffusion occur across membranes?

Answer 8

yes if:

• there is a concentration gradient
• and the membrane is permeable to the particle

Question 9

Give an example of diffusion across a membrane.

Answer 9

• cell membranes are freely permeable to oxygen

- if there is a lower concentration of oxygen inside a cell than outside, it will diffuse into the cell

Question 10

Can cellulose diffuse across cell membranes?

Answer 10

no

Question 11

What are ‘partially permeable’ membranes?

Answer 11

membranes that allow some substances to diffuse through but not others

Question 12

What is ‘simple diffusion’?

Answer 12

when a substance moves (diffuses) between the phospholipid molecules in the membrane

Question 13

Some substances are unable to pass between phospholipids. What is needed to allow these substances to diffuse through membranes?

Answer 13

channel proteins

Question 14

State a feature of channel proteins.

Answer 14

they are specific - they only allow one type of substance to pass through

Question 15

Give an example of a channel protein. What does this channel allow through?

Answer 15

• chloride channels

- only chloride ions

Question 16

How can cells control which substances pass through their plasma membranes? What can cells not control? Why?

Answer 16

• by the types of channel protein that are inserted into the membrane
• the direction of movement
• facilitated diffusion always occurs from a region of higher concentration to a region of lower concentration

Question 17

What sort of processes are simple and facilitated diffusion? Why?

Answer 17

• passive processes

- no energy has to be used by the cell to make them occur

Question 18

Draw two diagrams: one of simple diffusion and one of facilitated diffusion. (p10)

Answer 18

-

Question 19

Give an example of a voltage-gated channel. What are they used for?

Answer 19

• potassium channel in axons (part of a neuron)

- to transmit nerve impulses

Question 20

What part of a neuron contains potassium channels? When are potassium channels used?

Answer 20

• the axon

- used during action potential

Question 21

When is the potassium channel closed? When do they open?

Answer 21

• when the axon is polarized

- in response to depolarization of the axon membrane

Question 22

What happens in a potassium channel in an axon in response to depolarization of the axon membrane?

Answer 22

• potassium channel opens, allowing K^+ ions to exit by facilitated diffusion

Question 23

What happens after K^+ ions have exited the axon via the potassium channel?

Answer 23

• K^+ ions leaving repolarizes the axon

Question 24

For how long do potassium channels remain open? What ‘shuts’ them?

Answer 24

• a very short amount of time

- a globular sub-unit blocks the pore and the channel then returns to its original conformation

Question 25

Drawing 3 diagrams, explain how a potassium channel in an axon behaves before, during, and after action potential. (p10)

Answer 25

draw 3 diagrams of a potassium channel in an axon in these conformations:

1. channel closed
2. channel briefly open
3. channel closed by ‘ball and chain’