3.2.3 Transport Across Cell Membranes Flashcards
What’s diffusion
The movement of a substance (gas/liquid) from a high concentration to a low concentration.
What type of process is diffusion
What does it not require
It’s a passive process
It doesn’t require ATP
5 factors that affect the rate of diffusion
Concentration gradient Temperature Surface area Thickness of membrane Distance
5 ways lungs are adapted to allow rapid oxygen exchange between air in the alveoli and blood in the capillaries around them
Many alveoli + capillaries so large surface area
Good blood supply around alveoli
Short diffusion path
Ventilation - maintains conc gradient
Flattened epithelium
Concentration gradient - faster diffusion
How can different substances cross a cell surface membrane
Diffusion
Osmosis
Active transport
Facilitated diffusion by carrier proteins
Why will only some things pass through plasma membranes
As they’re semi-permeable
3 factors that affect the permeability of the cell membrane
Temperature
pH
Ethanol
How does temperature affect the permeability of membranes
Denatures channel/transport proteins
What does ethanol do to membrane permeability
It causes permeability to increase as phospholipids are soluble in alcohol
What type of molecule must you be to diffuse through phospholipids
A small molecule (tight together) without a charge
What cells are more succeptible to water damage and why
Animal cells as they have no cell wall
What molecules need to use facilitated diffusion to pass through the bilayer
E.g
Molecules that aren’t soluble in lipids
Glucose, amino acids (too big), urea, ions
What does facilitated diffusion use
Proteins in the membrane
2 types of proteins involved in facilitated diffusion
Channel proteins
Carrier proteins
How do carrier proteins allow insoluble substance into cell
Changes shape
What type of process is using carrier proteins in facilitated diffusion
What isn’t used
Passive
ATP isnt used
Where does the energy come from in facilitated diffusion with carrier proteins
The molecules’ kinetic energy
What do carrier proteins have specific for certain substances
Binding sites
When substance is attached to carrier protein what does it do
Flips + changes shape
What’s a Channel protein like
Tube with hole in (tunnel) that’s full of fluid
What molecules do channel proteins allow through
Larger molecules
What’s needed for movement via channel proteins
Concentration gradient (high->low concentration)
Define osmosis
The passive diffusion of water molecules down concentration gradient through a semi permeable membrane from high water potential -> low water potential
What’s the movement like in isotonic solutions
What’s the cell like
No movement (equilibrium) as it has the same water potential as cell
Cell is normal (flaccid)
