membranes Flashcards
what are membranes made of
phospholids in bilayers
what is the head of a phodpholipid
polar (hydrophillic)
what is the tail of a phospholipid
non polar (hydrophobic)
what is the hydrophobic tail made of
fatty acids and lipids
what is the model of the cell membrane called
fluid mosaic model
how is the membrane fluid
some parts are not attached to any other part of the cell and so can move freely
why is the membrane described as mosaic
because of the different sizes of phospholipids proteins and cholestrol
what is the purpose of cholesterol in the membrane
makes membrane more rigid and stable
what is the purpose of the glycoproteins/lipids
act as hormone receptors or cell to cell proteins
what is an extrinsic protein
only in the half of the membrane which is hydrophillic
what is an intrinsic protein
through all of the membrane
how do small and non polar molecules get through the membrane
they diffuse through the lipid bilayer
how do other molecules get through the membrane
some are too big or polar and so can’t go through the lipid bilayers, instead they go through hydrophillic channel or carrier proteins.
what is the difference between a channel protein and a carrier protein
channel - have a hydrophilic pore which can be open and closed carrier - have a binding shape for the molecule. they change their shape to allow the molecule to cross the membrane
what is diffusion
movement of molecules from an area of higher concentration to an area of lower concentration
what is osmosis
movement of water molecules from an area go high concentration of water to an area of low concentration of water through a partially permeable membrane
what is a solvent
a substance that a chemical can dissolve in
what is a solute
the molecule that dissolves
what is water potential
a measure of free energy of water molecules and the tendency of water to movw
what is water potential measured in
kPa (kilopascals)
water moves from a less negative………
water potential to a more negative water potential
what is the water potential in a dilute solution
more water potential energy
what is the water potential in a concentrated solution
less water potential energy
what is solute potential
how easily water molecules move out of a solution the more solute present the tighter the water molecules are held
what is pressure potential
pressure builds up within a plant cell due to the cell wall making the plant turgid. this pressure is pressure potential, resisting more water entry
what is the sign (+ or -) of pressure potential
+
water potential =
pressure potential + solute potential
what does it mean in a cell is hypertonic (plant and animal)
(plant)it is plasmolyse, the cell membrane is pulling away from the cell wall (animal) it will crenate it means that to much water is leaving the cell when in a concentrated solution in order to balance the amount of water outside the cell to the amount of water inside the cell
what does is mean if a cell is isotonic
it remains the same as water leaves in equal parts
what does it mean if a cell is hypotonic (plant and animal)
there is more water outside the cell than there is inside so more water will try and enter but the pressure potential will increase (plant) the cell wall will push out making the cell turgid(animal) the cell will explode as it has no cell wall to protect it and cant cope with the pressure
what is incipient plasmolysis
when the water potential outside and inside a cell is equal there is no net movement half of the cell is plasmolysed and half is not
what is ficks law
rate of diffusion is in proportion to (surface area x concentration gradient) / length of diffusion pathway
why is the rate of diffusion only ‘in proportion to’ and not equal to
because there are other factors that affect the rate of diffusion
what other factors affect the rate of diffusion
tempertaure size of diffusing molecules chemistry of diffusing molecules (polar or non polar)
what is active transport
molecules move from a low concentration to a high concentration against the concentration gradient
what does active transport need to take place
ATP for energy
