3.2.3 transport across cell membranes Flashcards
what is the cell surface membrane made up of?
phospholipid bilayer
what is the structure of a phospholipid?
hydrophilic head
- attracted to water and forms intermolecular forces with water.
hydrophobic tails
- rebelled by water.
what are the functions of the cell surface membrane?
- forms an impermeable barrier to polar substances, making it selectively permeable so non-polar substances can pass through.
- allows cells to maintain different concentrations on either side.
- makes membrane fluid, so it can fuse with other membranes and make membranes.
- gives flexibility and fluidity, as phospholipids can move laterally and rotate.
what type of molecules does the cell surface membrane allow through?
- small.
- uncharged.
- non-polar.
why is the cell surface membrane called the fluid mosaic model?
- as phospholipids move.
- there is a mixed pattern of the cell surface membrane.
where can you find cholesterol in the cell surface membrane?
- within the phospholipid bilayer.
what is the function of cholesterol?
- to prevent leakage of water and dissolved ions from cells, due to cholesterol being very hydrophobic.
- reduces membrane fluidity by reducing the movement of other molecules including phospholipids.
what is the difference between an intrinsic and extrinsic protein?
intrinsic = embedded within cell surface membrane.
extrinsic = outside the membrane.
what is the function of proteins?
act as receptors, signalling molecules, increasing membrane stability (providing strength and structure).
what are channel proteins?
has a water-filled tube to allow water-soluble ions to diffuse across.
transports mainly charged ions.
what are carrier proteins?
molecules (like glucose or amino acids) bind to carrier protein and then changes shape enabling movement of molecules across membranes.
what are glycolipids?
phospholipids with a carbohydrate chain.
what is the function of glycolipids?
- carbohydrate chain acts as a cell surface membrane receptor.
- act as recognition and attachment sites.
what are glycoproteins?
extrinsic protein with an attached carbohydrate chain.
what is the function of glycoproteins?
act as cell recognition, signalling and cell attachment sites.
what is the definition of simple diffusion?
the net movement of molecules from an area of high concentration to an area of low concentration through a phospholipid bilayer.
PASSIVE MOVEMENT
what type of molecules can move and pass through for simple diffusion?
- non-polar.
- small.
- non-charged.
what are the key requirements for simple diffusion?
- all particles in constant motion.
- random motion.
- particles bouncing off each other.
what is the definition of facilitated diffusion?
the passive movement (high to low concentration) across transmembrane channels (channel or carrier proteins).
DOES NOT REQUIRE ATP.
what type of molecules move via facilitated diffusion?
- large.
- polar.
- charged.
what can increase the rate of facilitated diffusion?
- concentration and number of proteins.
what is the definition of active transport?
the net movement of particles from an area of low concentration to high concentration against the concentration gradient.
REQUIRES ATP.
how does active transport work involving carrier proteins?
- the molecules/ions bind to a receptor on the channel of a carrier protein.
- ATP binds to the protein and splits into ADP and Pi.
- the carrier protein changes shape to transport the molecule or ion from one side of the membrane to the other.
- the Pi molecule is released from the protein and the protein reverts back to its original shape.
- ADP reforms ATP (respiration).
what is exocytosis?
out of cell, via vesicle.
what is endocytosis?
into cells.
- pinocytosis (adding fluid).
- phagocytosis.
what is the definition of osmosis?
the diffusion of water from a region of higher water potential to a region of lower water potential across a partially permeable membrane.
what is the definition of water potential?
the ability/ potential for water molecules to move freely.
what effect does adding solute have on the water potential of a solution?
adding solute decreases the number of water molecules moving freely, therefore decreasing water potential.
what is the water potential of a solution of pure water?
pure water = highest water potential = 0kPa
THEREFORE all other solutions will have a negative water potential.
what is a hypertonic solution?
when there is a net movement of water out of the cell as the solution has a lower water potential.
what is an isotonic solution?
when there is no net movement of water as the cell and solution have the same water potential.
what is a hypotonic solution?
when there is a net movement of water into the cell as the solution has a higher water potential.
what is the equation for water potential in plants?
water potential = osmotic solute potential + turgor hydrostatic pressure
what do plant cells look like in a hypertonic solution?
PLASMOYLSED
what do plant cells look like in an isotonic solution?
FLACCID
what do plant cells look like in a hypotonic solution?
TURGID
what is required for rapid osmosis of water in phospholipids?
rapid movement requires channel proteins.
what is co-transport and how can the movement be described?
- movement of 2 substances simultaneously through carrier protein.
= one substance moves via active transport against the conc gradient.
= one substance moves via facilitated diffusion down the conc gradient.
how do you increase the rate of transport across membranes?
- increase the number of CHANNEL & CARRIER PROTEINS.
- increase the SURFACE AREA of the membrane.
- increase CONCENTRATION GRADIENT.
- increase the number of MITOCHONDRIA to supply ATP.
