Diffusion Flashcards
Define diffusion.
The net movement of molecules or ions from a region where they are more highly concentrated to a region where their concentration is lower until they reach a dynamic equilibrium.
What does ‘dynamic equilibrium’ mean?
A state of balance in continuing processes - in diffusion a dynamic equilibrium is reached where the molecules/ions are evenly distributed.
Why do charged ions and polar molecules find it difficult to diffuse across the membrane?
Because of the hydrophobic nature of the fatty acid tails of the phospholipids in the membrane.
What type of process is facilitated diffusion?
Passive. It relies only on the kinetic energy of the diffusing molecules.
How does facilitated diffusion differ from diffusion?
It can only occur at specific points on the plasma membrane as it relies on channel and carrier proteins.
Describe protein channels.
Are water-filled, hydrophilic channels in the membrane. Allow only specific water soluble ions to pass through. i.e. only open for certain ions so there is control over entry and exit of ions.
How do protein channels work?
An ion binds with the protein which causes it to change shape in a way that closes it one side of the membrane and opens it up the other side.
Describe carrier proteins.
When a molecule specific to the protein binds with the protein, it causes the protein to change shape in such a way that the molecule is released to the inside of the membrane.
