2: CELLS - TRANSPORT Flashcards
(40 cards)
What is diffusion?
the net movement of particles from an area of high conc to an area of low conc/down the conc gradient
Is diffusion an active/passive process?
passive
What are the factors affecting rate of diffusion?
- conc gradient (the higher the conc gradient the higher the rate of diffusion)
- thickness of exchange surface (the thinner the exchange surface the faster the rate of diffusion)
- surface area (the larger the surface area the faster the rate of diffusion)
Why does diffusion slow down over time?
as diffusion takes place the difference in conc between the 2 sides of the membrane decreases until it reaches equilibrium therefore diffusion slows down over time
What is facilitated diffusion?
diffusion where transport proteins are needed for large/polar molecules to diffuse across a membrane
What are the 2 types of transport proteins present in cell membranes?
- channel proteins
- carrier proteins
What type of molecules are transported across a membrane by carrier proteins?
large molecules
How do carrier proteins facilitate the diffusion of large molecules?
- a large molecule attaches to a carrier protein in the membrane
- the protein changes shape which releases the molecule on the other side of the membrane
- different carrier proteins facilitate the diffusion of different charged particles
What type of molecules are transported across a membrane by channel proteins?
polar molecules/ions
How do channel proteins facilitate the diffusion of ions/polar molecules?
- form pores in the membrane for charged particles to diffuse through (some are gated meaning that they open and close in response to stimuli)
- different channel proteins facilitate the diffusion of different charged/polar molecules
What is Fick’s law?
rate of diffusion is directly proportional to the (surface area x the conc difference) / the thickness of the membrane
What is osmosis?
the net movement of water molecules from an area of high water potential to an area of low water potential across a partially permeable membrane
What are the factors affecting rate of osmosis?
- water potential gradient (the higher the water potential gradient the higher the rate of osmosis)
- thickness of exchange surface (the thinner the exchange surface the faster the rate of osmosis)
- surface area (the larger the surface area the faster the rate of osmosis)
What is water potential?
the tendency of water to move from 1 place to another by osmosis
What is water potential measured in?
kPa
What is the water potential of distilled/pure water?
0kPa (highest water potential)
Why does pure/distilled water have a water potential of 0kPa?
highest conc of freely moving water particles
Why do all solutions have a -ve water potential?
lower conc of freely moving water molecules (relative to water)
How does conc of solutes affect water potential of a solution?
the higher the solute conc, the more -ve the water potential
What are aquaporins?
channel proteins that are specific to water and facilitate osmosis
Explain what you would expect to happen when visking tubing containing a concentrated sugar solution is placed in distilled water (4 marks)?
- water moves by osmosis into the visking tubing causing the visking tubing to swell
- water moves from a high water potential (0kPa) into the concentrated solution with a lower water potential across the visking tubing which acts as a partially permeable membrane
What is an isotonic solution?
a solution with the same water potential as the cell
What would happen to a cell in an isotonic solution?
won’t lose/gain any water as there is no difference in water potential
What is a a hypotonic solution?
a solution with a higher water potential than the cell
