1. Diffusion and Facilitated Diffusion Flashcards
What are the 3 states of matter?
solids, liquids and gases
What are solids, liquids and gases made up of?
particles - atoms, ions and molecules
Describe the movement of particles in liquids and gases.
continual random* motion
- the direction of movement is random
What is the case if there is ‘no net movement’ of particles in a liquid or gas?
they are evenly spread and remain evenly spread despite continually moving
What is the case if particles are unevenly spread? What does this cause?
- there is a higher concentration in one region than another
- diffusion
Define ‘diffusion’.
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
Why does diffusion occur?
because more particles move from the region of higher concentration to the region of lower concentration than in the opposite direction
Can diffusion occur across membranes?
yes if:
- there is a concentration gradient
- and the membrane is permeable to the particle
Give an example of diffusion across a membrane.
- 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
Can cellulose diffuse across cell membranes?
no
What are ‘partially permeable’ membranes?
membranes that allow some substances to diffuse through but not others
What is ‘simple diffusion’?
when a substance moves (diffuses) between the phospholipid molecules in the membrane
Some substances are unable to pass between phospholipids. What is needed to allow these substances to diffuse through membranes?
channel proteins
State a feature of channel proteins.
they are specific - they only allow one type of substance to pass through
Give an example of a channel protein. What does this channel allow through?
- chloride channels
- only chloride ions
How can cells control which substances pass through their plasma membranes? What can cells not control? Why?
- 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
What sort of processes are simple and facilitated diffusion? Why?
- passive processes
- no energy has to be used by the cell to make them occur
Draw two diagrams: one of simple diffusion and one of facilitated diffusion. (p10)
-
Give an example of a voltage-gated channel. What are they used for?
- potassium channel in axons (part of a neuron)
- to transmit nerve impulses
What part of a neuron contains potassium channels? When are potassium channels used?
- the axon
- used during action potential
When is the potassium channel closed? When do they open?
- when the axon is polarized
- in response to depolarization of the axon membrane
What happens in a potassium channel in an axon in response to depolarization of the axon membrane?
- potassium channel opens, allowing K^+ ions to exit by facilitated diffusion
What happens after K^+ ions have exited the axon via the potassium channel?
- K^+ ions leaving repolarizes the axon
For how long do potassium channels remain open? What ‘shuts’ them?
- a very short amount of time
- a globular sub-unit blocks the pore and the channel then returns to its original conformation
Drawing 3 diagrams, explain how a potassium channel in an axon behaves before, during, and after action potential. (p10)
draw 3 diagrams of a potassium channel in an axon in these conformations:
- channel closed
- channel briefly open
- channel closed by ‘ball and chain’
