Lecture 11 Flashcards
What is diffusion?
Process where a concentration difference between regions is minimised as a result of spontaneous flow of matter.
Also regarded as the mass transfer of individual molecules due to random motion as a result of the concentration gradient between the two regions.
What is the driving force of diffusion?
concentration gradient
Why can diffusion be seen in gas, liquid, and dissolved solutes?
These all have a spontaneous tendency to distribute itself uniformly over the space available.
What do drug absoprtion, elmination, nutrient transport in living tissues and biological membranes all require in order to take place?
diffusion
What is a membrane?
Physical barrier/film which separates two distinct compartments where the material passes through either by passive, active of facilitated transport.
what are the 3 types of membranes?
Membrane of dense material with straight through pores. Found in filter barriers like nucleopore
Homogenous membrane without pores
Cellulose membrane used in filtration showing intertwining nature of fibres and tortuous channels
what is a semi permeable membrane?
membrane which is permeable to only certain molecules and not all.
What is a barrier?
Region/(s) of a system that creates resistance to mass transfer or diffusion,
E.g. Stirring to help dissolve the salt in a cup of water.
What is the importance of fick’s law?
Can describe a diffusion process
What are the criteria of fick’s law?
concentration gradient doesn’t change with time or distance
This is also known as diffusion under a steady state.
Fick’s first law can describe the diffusion process in this situation.
What is flux proportional to? (in fick’s first law)
the concentration gradient
what is flux?
the amount of material transferred through per unit cross section area in unit time
units = gcm-2sec-1 or molcm-2sec-1
Is flux a positive or negative value?
Flux is always a positive value
The negative sign only tells use that the flux is in the direction of the decreasing concentration (diffusion is movement of particles from an area of high concentration to an area of low concentration)
What is the diffusion coefficient (D) affected by?
temperature, pressure, chemical nature of solute, solvent properties
it doesnt normally remain constant
What happens in a non-steady state of diffusion?
in many systems, concentration varies with both time and distance so we cannot apply fick’s first law as it is an unsteady state
we can apply fick’s second law
