3.2 Diffusion Flashcards
What is diffusion?
The net movement of molecules/ions down the concentration gradient from an area of high concentration to an area of less concentration until they are evenly distributed.
What is simple diffusion?
a passive method of transport across the cell membrane via the phospholipid bilayer, involving non polar molecules.
What are polar molecules soluble in?
Non polar?
Polar are water soluble.
Non-polar are fat soluble.
How does concentration gradient affect rate?
The bigger the difference, the faster the rate.
How does surface thickness affect the rate of diffusion?
If it is a thinner surface, the distance to be travelled is less so the rate is faster.
Surface area?
the larger the surface area, the greater the chance of colliding with a boundary so the rate is faster.
What molecules can diffuse across the plasma membrane?
what is this known as?
small non-polar molecules such as oxygen or carbon dioxide.
this is simple diffusion.
What is facilitated diffusion?
a passive method of transport accross membranes involving carrier proteins and channel proteins.
Which molecules are involved in facilitated diffusion?
Charged ions or polar molecules which have to be aided by protein channels or carrier proteins.
What are protein channels?
water filled hydrophilic channels which allow water soluble ions to pass through.
what are protein channels to particular ions?
they are specific or complementary to them.
Why does the protein channel close if the ion it is specific to isn’t present?
to control the entry and exit of ions.
What happens when the ion binds with the protein?
the protein changes shape and the membrane closes on one side and opens on the other.
what are carrier proteins?
they are specific/complementary to molecules.
what do carrier proteins do when a molecule such as glucose is present?
it binds to the protein, which causes a change of shape to the protein so the glucose is released on the other side.
How does concentration gradient affect the rate of facilitated diffusion?
the greater the gradient, the faster it can occur.
How does the number of carrier proteins or protein channels affect the rate of FD?
once all proteins are being used, the rate cannot occur any quicker even if the gradient increases.
why must glucose be absorbed by co-transport?
the concentration of glucose in the ileum is too low for it to diffuse into the blood by diffusion.
what does the sodium-potassium pump bind?
3 sodium ions & a molecule of ATP.
what does the splitting of ATP provide in the sodium-potassium pump?
the energy to change the shape of the channel, the sodium ions are driven through it.
where are the sodium ions released to?
the outside of the membrane, and the new shape of the channel allows 2 potassium ions to bind.
what does the release of the phosphate on the sodium-potassium pump allow?
the channel to revert to its’ original form, which releases the potassium ions on the inside of the membrane.
where are sodium ions actively transported out of and what does this cause?
out of the epithelial cells in the ilium, into the blood, by the S-P pump. this causes a concentration gradient because there is now a higher concentration of sodium ions in the lumen of the ileum than inside the cell.
what does the higher concentration gradient of sodium in the lumen cause?
sodium ions to diffuse from the lumen of the ileum into the epithelial cell, down the concentration gradient.
what does the co-transporter carry regarding movement of sodium from the lumen into the epithelial cells?
glucose into the cell with the sodium which causes the concentration of glucose inside the cell to increase.
what happens to the glucose once it has been carried into the cell with the sodium?
it diffuses out of the cell into the blood, down its’ CG through a protein channel by facilitated diffusion.
what type of transport are carrier proteins involved in?
active transport and facilitated diffusion.
what type of transport are channel proteins involved in?
facilitated diffusion
