Transport Across Cell Membranes Flashcards
(28 cards)
What is diffusion (simple)?
The net movement of molecules or ions from an area of high concentration to an area of lower concentration until equilibrium reached. (This is a passive process so it relies on kinetic energy, not ATP.)
What is facilitated diffusion?
When charged ions/polar molecules move across the cell surface membrane, relying on intrinsic proteins. It is a passive process and occurs down a concentration gradient.
What is a channel protein?
A protein that is a hydrophilic water-filled channel across the membrane which allows specific water soluble ions to pass. It is selective for a specific ion that bonds and causes a conformational change in shape.
What is an aquaporin?
A channel protein for water only.
What is a carrier protein?
An intrinsic protein which a specific molecule binds to , causing a change in shape which releases that molecule inside.
What is a co-transport protein?
A carrier protein that allows more than 1 molecule to move, e.g. glucose-sodium co-transport protein.
What does the rate of diffusion depend on?
- Concentration gradient
- Thickness of exchange surface
- Surface Area
- Temperature
- Stirring/moving
- Size of molecule
- Increase in channel/carrier proteins (facilitated diffusion)
What is a partially permeable membrane?
A membrane which only allows some substances through.
What is osmosis?
The movement of water from a region of higher water potential to a region of lower water potential across a partially permeable membrane.
What is water potential?
Pressure on cell membrane caused by water molecule collisions.
How does the amount of solutes dissolved affect water potential?
It makes it more negative.
What does isotonic mean?
When the concentration of solutes is equal in and outside of the cell.
What does hypertonic mean?
Where the concentration of solutes in the solution is greater outside the cell than inside. (e.g. high sugar concentration)
What does hypotonic mean?
Where the concentration of solutes in the solution is greater inside the cell than outside. (e.g. pure water)
What happens when an animal cell is placed in a hypertonic solution?
The cell shrinks and shrivels.
What happens when an animal cell or a plant cell is placed in an isotonic solution?
There is no change.
What happens when an animal cell is placed in a hypotonic solution?
The cell swells and bursts. (can be described as being haemolysed if the cell has a haem group, e.g. erythrocyte [red blood cell])
What happens when a plant cell is placed in a hypertonic solution?
The cell is plasmolysed (the cell membrane pulls away from the cell wall).
What happens when a plant cell is placed in a hypotonic solution?
The cell becomes turgid.
What factors influence the movement of water into and out of cells?
- The concentration of solutes.
- The amount of water present in the cytoplasm and the exterior environment.
- The presence of aquaporins membranes.
- (Plants) The pressure exerted on cell contents by cell wall, which is rigid and resists expansion, and therefore uptake of water.
What is active transport?
The movement of molecules or ions from a region of lower concentration to a region of higher concentration (against a concentration gradient) using ATP and carrier proteins.
Describe active transport.
- Molecule or ion binds to specific receptor site on carrier protein
- ATP binds to protein causing ATP -> ADP + Pi
- Protein changes shape + molecule/ion released inside
- Phosphate (Pi) released from protein, causing protein to return to original shape. Pi recombines ADP -> ATP in respiration
Why are membrane described by the ‘fluid mosaic model’?
‘Fluid’ refers to the lateral, fluid movement of phospholipids and ‘mosaic’ refers to the different proteins embedded in the phospholipid bilayer.
What do phospholipids allow the membrane to be?
Flexible and self sealing.
