Methods Used To Transport Molecules Through Cell Membranes Flashcards
What are the 5 methods to move substances in or out of cells?
- diffusion
- facilitated diffusion
- osmosis
- active transport
- endocytosis and exocytosis
Describe how diffusion works
- net movement of molecules from high to low conc across a partially permeable membrane
- passive process so doesnt require energy
- stops when molecules have reached equilibrium
- involves non - polar, small and lipid soluble molecules e.g oxygen and CO2
What is the equation for ficks law ( rate of diffusion )?
(Surface area x conc gradient) / diffusion distance
What are the 4 factors affecting rate of diffusion?
- surface area
- conc gradient
- temperature
- diffusion distance
How does temp affect rate of diffusion?
- increased kinetic energt
- faster rate of diffusion
How does surface area affect rate of diffusion?
- larger S.A = more space for molecules to pass thru, so faster ROD
- allows more proteins to be present
How does conc gradient affect rate of diffusion?
- as conc diff inc, rate of diffusion inc
How does diffusion distance affect rate of diffusion?
- the shorter the diffusion difference (thinner membrane)
- the faster molecules will travel thru it
Describe how facilitated diffusion works
- diffusion used when proteins help some molecules to pass thru phospholipid bilayer
- hydrophilic substances cant pass thru hydrophobic tails of bilayer
- as fatty acid tails are non - polar so repel polar molecules
- so to enter/exit cell, water soluble molecules need to move thru membrane via channel or carrier proteins
- these are a specific shape so only transport specific molecules complementary to binding site
ALL PROTEINS HAVE BINDING SITES, only enzymes have active sites
What do all proteins have in terms of sites?
ALL PROTEINS HAVE BINDING SITES, only enzymes have active sites
Explain why facilitated diffusion would level off/plateau at a lower rate?
- carrier/channel proteins binding sites are full or saturated
- causing it to plateau at a lower rate as there are fewer specific carrier proteins for this molecule in membrane
- number of proteins becomes limiting factor
Describe how osmosis works
- net movement of water molecules from a low to high concentration of water across a partially permeable membrane
- passive process, doesnt require energy
What affect would a lower solute concentration than tissue/organelle have on cells, in terms of osmosis?
Animal cells - swelling + lysis (bursting)
Plant cells - swell, inc mass, (cellulose wall prevents lysis)
- Water moves in by osmosis
What affect would a higher solute concentration than tissue/organelle have on cells, in terms of osmosis?
Animal cells - shrivelling
Plant cells - membrane pulls away from cell wall
- water moves out by osmosis, mass is lost
What affect would a isotonic (equal) solute concentration than tissue/organelle have on cells, in terms of osmosis?
- no net movement of water in and out of cells, no osmosis
- solute conc inside and outside of cell is at an equilibrium
- no conc gradient = no gain in mass
Describe how active transport works
- used to transport molecules across membrane against their conc gradient
- from low to high conc
- requires specifically shaped carrier proteins with a complementary binding site that only complementary molecules bind to
- requires energy supplied by ATP which is produced during respiration, it is an ACTIVE process
What are two other forms of active transport?
Exocytosis and endocytosis
Describe what happens during exocytosis
- uses golgi vesicles to move large quantities of molecules such as enzymes/nts
- from inside to outside of the cell
- ATP is required to move the vesicles
- vesicles fuse with membrane
Describe what happens in endocytosis
- cell surface membrane is pulled inwards to create a vesicle
- any molecules within this area are enclosed within vesicle
- the movement of vesicle into the cell also requires the breakdown of ATP into ADP and Pi
