Diffusion Flashcards
In what two ways does the exchange of substances occur?
In ways that require metabolic energy and ways that are passive.
Describe simple diffusion.
The transport of small, non-polar, lipid soluble molecules across the bilayer without external input of ATP energy, down a concentration gradient.
Define diffusion.
The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed.
What type of molecule can diffuse across membranes easiest?
Small, non-polar molecules, for example oxygen and carbon dioxide.
Why do charged ions and polar molecules not diffuse well?
Because of the hydrophobic nature of the fatty-acid tails in the phospholipids in the membrane.
What is facilitated diffusion?
Diffusion that involves protein channels and carrier proteins.
How is facilitated diffusion a passive process?
It relies only on the inbuilt motion (kinetic energy) of the diffusing molecules. There is no external input of ATP from respiration.
How does facilitated diffusion differ from passive diffusion?
It occurs at specific points where there are special protein molecules.
What do protein channels form across the membrane?
Water-filled hydrophilic channels across the membrane.
In what way are protein channels selective?
Channels each open in the presence of a specific ion.
How does the protein channels allow the ion through?
The ions bind with the protein causing it to change shape in a way that closes it to one side of the membrane and opens it to the other.
Where do carrier proteins span?
They span the plasma membrane.
How does a Carrier protein work?
The molecule binds to the protein causing it to change shape in way that releases the molecule inside the cell.
What energy does facilitated diffusion use?
kinetic energy.
Star three factors that affect the rate of diffusion.
Temperature, SA:V, concentration gradient, diffusion distance.
