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)
What’s osmosis like in hypotonic solutions
What happens to cell
Hypotonic has higher water potential than cell so water goes into cell
It swells (turgid)
What’s osmosis like in hypertonic solutions
What happens to cell
Hypertonic has lower water potential than cell so water leaves the cell
It shrivels (dehydrated + plasmolyzed)
What are aquaporins
Proteins that transport water (in membrane)
Define active transport
Movement of substances against a concentration gradient from low -> high concentration
What does scribe transport require to work (2)
Energy from ATP
Transport proteins in membrane
What pump is an example of active transport
Sodium-potassium pump
How does the sodium potassium pump work (6)
- Sodium in cell bonds to transport protein
- ATP attatches to protein and is hydrolysed
- The releases energy
- Allowing protein to change shape to allow sodium out of cell
- Potassium ions outside cell bind to protein
- Phosphate group is released + protein returns to original allowing potassium into cell
What’s ATP hydrolysed into
ADP + P
What does energy released from hydrolysis of ATP in sodium-potassium pump allow
Allows protein to change shape to allow sodium out of cell
What is moved in 1 cycle of the sodium-potassium pump
3 sodium out of cell
2 potassium’s into cell
3 examples of active transport
In small intestine moves glucose to and from blood
Plants move minerals out of soil
Sodium-potassium pump
What’s water potential (osmosis) measured in
KPa
How many KPa is the highest water potential (pure water)
0KPa
What numbers are lower water potentials
Negatives
What proteins may osmosis involve
Aquaporins
What are solutes
What is getting dissolved in a solvent to form a solution
What curve can estimate an unknown value
Calibration curve
What’s co-transport
What’s it a type of
Moving 2 Substances at the same time
Facilitated diffusion
What’s the pump for co-transport in the small intestine
The sodium-glucose symporter
What has to be done in the sodium-glucose symporte rbefore the molecules can be moved by the protein
Both sodium + glucose must bind
What makes it easier for the other molecule to bind in the sodium-glucose symporter
The binding of 1 molecule
What keeps the sodium-glucose symporter moving in the right direction
The sodium concentration gradient
What would happen due to the sodium-glucose symporter if sodium levels in epithelial cells were allowed to accumulate
How would this allow the co-transport of glucose
Sodium would be actively pumped out of the epithelial cells and into the blood by Na/K+ pump
As this maintains the concentration gradient for glucose to pass into the blood via facilitated diffusion
What’s the end of the small intestine called
The ileum
