Diffusion Flashcards
Define Diffusion
The net movement of particles (molecules or ions) from an area of higher concentration to an area of lower concentration
What does diffusion continue until
Particles are evenly distributed throughout liquid/gas
What is the concentration gradient in diffusion
the path from an area of higher concentration to an area of lower concentration
What way do particles diffuse via the concentration gradient in diffusion
Down the concentration gradient
Does diffusion require energy?
No, it is a passive process
Can particles diffuse across cell membranes?
Yes, as long as they can move freely through the membrane
What is it known as when molecules diffuse directly through a membrane
Simple diffusion
Is rate of diffusion always the same
No
What does rate of diffusion across membranes depend on
Concentration gradient, thickness of the exchange surface and surface area
How does the concentration gradient effect the rate of diffusion across a membrane
The higher it is, the faster the rate of diffusion. As diffusion takes place, the difference in concentration between the two sides of the membrane decreases until it reaches an equilibrium. This means diffusion slows over time.
How does the thickness of the exchange surface effect the rate of diffusion across a membrane
The thinner the exchange surface, the faster the rate of diffusion (shorter distance particles must travel).
How does the surface area effect the rate of diffusion across a membrane
The larger the surface area (e.g. cell surface membrane) faster rate of diffusion.
Why would larger molecules (e.g. amino acids, glucose) diffuse extremely slowly through the phospholipid bilayer
Because they are so big
Why would charged particles (e.g. ions and polar molecules) diffuse extremely slowly through the phospholipid bilayer
Because they are water soluble, and the centre of the bilayer is hydrophobic.
How do large or charged particles speed things up and diffuse through the bilayer
They diffuse through carrier proteins or channel proteins in the cell membrane - this is called facilitated diffusion
What way does facilitated diffusion move particles across the concentration gradient
Down
How do carrier proteins diffuse large molecules
First a large molecule attaches to a carrier protein in the membrane.
Then, the protein changes shape
This releases the molecule on the opposite side of the membrane.
How do channel proteins diffuse charged particles
Channel proteins form pores in the membrane for charged particles to diffuse through (down concentration gradient). Different channel proteins facilitate diffusion of different charged particles.
What are the factors affecting the rate of facilitated diffusion
Concentration gradient, number of channel/carrier proteins
How does concentration gradient effect the rate of facilitated diffusion
The higher the concentration gradient, the faster the rate of facilitated diffusion (up to a point). As equilibrium reached rate of facilitated diffusion will plateau.
How does number of channel / carrier proteins effect the rate of facilitated diffusion
Once all the proteins in a membrane are in use, facilitated diffusion can’t happen any faster, even if you increase the concentration gradient.
How do you calculate the rate of diffusion
Draw a tangent on the graph, find change in y and change in x on tangent and do: change in y/change in x
