Cellmembranes and transport Flashcards
Phospholipids structure.
Phosphate head - polar - hydrophylic - soluble in water
Fatty acid tail - non-polar - hydrophobic - insoluble in water.
What is a phospholipid monolayer?
where Phospholipids spread over the surface of water and form a layer
Phospholipid bilayer also contains protiens. Name the two types and explain
Intrinsic embeded in the membrane - arrangement determined by their hydrophilic and hydrophobic regions
Extrinsinc on the outer or inner surface of the membrane
What is the fluid mosaic model?
Cell membranes are fluid because the phospholipids and protiens can move around via diffusion
mosaics because the scattered pattern produced by the protiens within the phospholipid bilayer looks somewhat like a mosaic from above
Cholesterol in the cell surface membrane.
cholesterol molecuels have a hydrophobic tail and hydrophylic head
fit between phospholipid molecules and oriented the same way (head out, tail in)
are absent in prokaryotes membranes.
restrics the movement of other molecules making up the membrane
Glycolipids in cell surface membrane
lipids with carbohydrate chains attached.
chains project out into whatever fluid is surrounding the cell. (found in the outer phospholipid monolayer)
Glycoprotiens use in the cell surface membrane
Protiens with carbohydrate chains attached. chains project out into whatever fluid surrounds the cell, found in the outer phospholipid monolayer
what are protiens which span the entire membrane called? with one example.
Transmembrane protiens
e.g. transport protiens
Facilitated diffusion, why needed, what uses it and what assists it?
Some substances cannot diffuse through the phospholipid bilayer.
Large polar molecules e.g. glucose and amino acids.
Ions such as sodium and chloride
Channel protiens and carrier protiens
highly specific, only allow one type of molecule or ion to pass through.
Channel protiens
water filled pores
allow charged substances to diffuse
not free, gated, protien inside moves to open and close the pore
this allows controled exchange of ions.
Carrier protiens
unlike channel protiens, they can switch between two shapes
this causes the binding site to pe open to one side of the membrane but not the other and then switch
net movement of particles will occur down a concentration gradient of the specific molecule.
How does a plant retain water and what happens if it can not?
Water will enter the plant cell through the partially permeable cell surface membrane by osmosis.
This is due to the higher water potential outside the cell.
Water enters the vacuole - incrase in plant cell volume.
Protoplast (living part of the cell inside the cell wall) pushes against the cell wall and pressure builds up inside the cell.
inelastic cell wall prevents bursting
The pressure createrd by the cell wall also stops too much water entering and this also helps to prevent the cell bursting
becomes fully turgid, rigid.
turgidity provides support and strength for the plant - stand upright with leaves held out to catch sunlight.
Without enough water, the cells can not remain rigid and firm and the pland wilts.
What happens if a plant cell is placed in a solution with lower water potential.
plant cell placed in concentrated sucrose solution
water will leave the plant through the partially permeable membrane by osmosis.
As water leaves the vacuole of the plant cell, volume decreases.
Protoplast gradually shrinks and no longer exerts pressure on the cell wall.
it now begins to pull away from the cell wall.
this is Plasmolysis
the plant is plasmolysed
What is a hypertonic solution?
Red blood cells have higher water potential than solution
net movement of water out
flacid cells.
any concentrated solution (sucrose)
What is an isotonic solution?
Water potential is equal between the red blood cell and solution
No net movement water.
Normal cells (healthy)
