1.4 - Membrane Transport Flashcards
Define simple diffusion
The passive movement of particles from an area of high concentration to low concentration using existing kinetic energy
Define osmosis
The passive movement of water molecules from an area of low solute concentration to high solute concentration across a partially permeable membrane using attraction between solute particles and water
Define active transport
the movement of particles against the concentration gradient using energy from ATP and carriers in the membrane
Define facilitated diffusion
substances that cannot pass through the phospholipid bilayer have to pass through integral protein channels that have a hydrophilic core
Simple diffusion (3)
- substances such as O2, CO2, H2O, lipids, steroids, hormones
- passive: no energy from ATP used
- EG: alveolar surface of lung (O2, CO2)
Facilitated diffusion using carriers (2)
- lipid-insoluble molecules
- EG: glucose into red blood cells
Facilitated diffusion using channels (3)
- small polar molecules and ions diffuse aided with channel proteins
- these create hydrophilic pores to allow channel-mediated facilitated diffusion
- EG: Na+ entering nerve cells
Osmosis (3)
- passive: no energy
- can move by simple or facilitated diffusion
- EG: water in roots
Give two examples of active transport and state what type of pumps they are
- sodium-potassium pump in neurons: symport
- sodium-chlorine pump in kidneys: antiport
What is required by active transport?
An integral protein transporter in the membrane
Give the steps of active transport (6)
- ATP binds to a transport protein
2a) Enzyme breaks covalent bond on one of the phosphates
2b) Molecule or ion binds to transport protein - The split releases enough energy to change the shape of the pump so that it opens outward
4a) Molecule or ion released
4b) Phosphate is released and process starts again
Exocytosis and endocytosis (4)
- types of active transport
- plasma membrane folds around a substance to transport it across the cell
- works due to the fluidity of the membrane
- vesicular transport/cytosis
Define exocytosis
The transportation of large materials or materials in bulk OUT OF a cell
What are the steps of exocytosis? (5)
- Materials needed are made in the ribosomes
- Then processed and packaged by the golgi apparatus
- These vesicles then move along the cytoplasm
- Fuse with the plasma membrane
- Materials are released
Give two examples of exocytosis
- Digestive enzymes
2. How nerve cells release neurotransmitters
Define endocytosis
The transportation of large materials or materials in bulk INTO a cell
What are the different types of endocytosis? (3)
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis
What are the steps of pinocytosis? (3)
- Part of the plasma membrane is pulled inwards
- Droplet of fluid becomes enclosed once vesicles bud off
- This then waves through the cytoplasm
Define hypertonic
A solution that has a higher osmolarity than another
Define isotonic
A solution that has the same osmolarity as another
Define hypotonic
A solution that has a lower osmolarity than another
Define osmolarity
A measure of the solute concentration in a solution
What type of solution must organs and tissues be kept in and why? (5)
- isotonic
- red blood cells have no cell wall
- they will wrinkle if placed in a hypertonic solution
- they will burst if placed in a hypotonic solution
- will stay the same in an isotonic solution
Who proposed the fluid-mosaic model and when?
Singer and Nicholson
1972
How was the fluid-mosaic model supported? (2)
- observations from electron microscope
- proteins were present on surface of phospholipids bilayer but not as a continuous layer
Who proposed the sandwich model and when?
Davison and Danielli
1935
Describe the sandwich model (2)
- phospholipid bilayer in the centre
- proteins coat both surfaces forming a ‘sandwich’
Give evidence for the sandwich model (3)
- 1959
- using electron micrograph and potassium permanganate.
- stain showed two dark lines and a pale line in between.
Name 3 problems with the sandwich model
- proteins would be exposed to hydrophilic surfaces on both sides which is unstable
- lipid soluble substances would not pass through
- membranes are bifacial (have different inner and outer surfaces)
