2. Cells - Transport Across Cell Membranes Flashcards
(12 cards)
Define simple 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 is the function of facilitated diffusion/why is it needed?
Charged ions and polar molecules do not diffuse easily because of the hydrophobic nature of the fatty-acid tails of the phospholipids in the membrane. The movement of these molecules can be made easier (facilitated).
Does facilitated diffusion require ATP? Explain why:
No external input of ATP, it relies only on the kinetic energy of the diffusing molecules.
What proteins are involved in facilitated diffusion?
Protein channels and carrier proteins.
What do protein channels form across the membrane?
Water-filled hydrophilic channels.
What do protein channels allow through?
Specific water-soluble ions.
How do protein channels maintain control over the entry and exit of ions?
The channels are selective, each opening in the presence of a specific ion. If the particular ion is not present, the channel remains closed.
What happens when the ions bind to the channel protein?
They cause it to change shape in a way that closes it to one side of the membrane and opens it to the other side.
How do carrier proteins work in facilitated diffusion?
When a molecule that is specific to the protein is present, it binds with the protein. This causes it to change shape in such a way that the molecule is released to the inside of the membrane.
Is ATP used in carrier proteins?
No, only the kinetic energy of the molecules themselves.
Define osmosis:
The passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selectively permeable membrane.
Define active transport:
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins
