5.3 DIFFUSION Flashcards
What is diffusion?
The net movement of anything from a region of higher concentration to a region of lower concentration
What is diffusion driven by?
a concentration gradient
What is a concentration gradient?
A change in concentration over a distance
What energy is required for diffusion and what is this process called?
Comes from internal kinetic energy of the particles - does NOT need external energy (ie.ATP)
It is a passive process
What is Brownian Motion?
A single molecule moving around randomly when suspended in a liquid or a gas - relies on the kinetic energy of the molecule
What happens when there are more molecules filling up a solution?
There is a statistical trend that the solute fills the container more and more uniformly
What happens when there is a larger number of solute molecules in a solution?
All randomness is gone, the solute appears to move smoothly from high concentration areas to low concentration areas.
What is the APPARENT force pushing molecules from high to low concentrations?
the Entropic force
Why is the entropic force apparent?
there is no actual microscopic force moving molecules down a concentration gradient - there only appears to be one
What are the key concepts of Fick’s Law?
Higher the temperature, higher the rate of diffusion
Higher the concentration difference, higher the rate of diffusion
Higher the surface area of the exchange surface, higher the rate of diffusion
Higher the membrane thickness, lower the rate of diffusion
What is equilibrium?
Once a concentration gradient has been equalised, equilibrium has been reached.
Particles do not stop moving - moving equally in all directions.
What is the difference between diffusion and bulk transport?
Diffusion is the moment of particles within other other particles down a concentration gradient,
Bulk Flow is the movement of a whole substance or all particles moving in one direction.
Give an example of bulk flow:
air inside alveoli due to a pressure gradient - high pressure outside the lungs and low pressure in the alveoli when breathing in, this bulk flow stops when the pressure is equalised in the alveoli.
Give an example of diffusion:
oxygen molecules in the air into blood due to a concentration gradient, the oxygen are the particles moving within all the other molecules in the air
e.g. nitrogen
What are the two types of diffusion?
simple diffusion
facilitated diffusion
What is simple diffusion?
-diffusion between phospholipids (across a membrane)
What molecules are able to use simple diffusion across a membrane?
-small and non-polar molecules eg. oxygen/co2
-water (small/polar molecule) can diffuse but slower due to the partial charges (delta +/-) being repelled by the hydrophobic core of the membrane.
What molecules find it difficult/can’t simple diffuse across a membrane?
-Large and Polar molecules eg. glucose
-Fully charged molecules or ions due to the charges being repelled by hydrophobic core
What can affect what goes through a membrane through simple diffusion?
Bigger the non-polar molecule, lower the rate of diffusion
What is facilitated diffusion?
Through a transmembrane protein
- channel/carrier
What is a carrier protein?
has a pore that is never fully open across the membrane, it changes shape when a specific molecule/ion binds to the protein
-has a lower rate of diffusion due to the limited pores available
-energy for this shape change does NOT come from ATP
What is a channel protein?
Has a permanently open pore/ pore that can open and close. this pore is specific to the molecule/ion
Has a high rate of diffusion but is saturable due to the limited pores available.
What are the pores made out of in transmembrane proteins?
alpha helix, in a polypeptide chain - R groups control what can go through
What is dialysis tubing?
artificial semi-permeable membrane tubing
- fine smooth membrane with holes in it (holes are large enough to fit water and other small molecules through but are too small to allow large molecules)
