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)
Hypotonic solution
Red blood cells have lower water potential than solution.
Net movement of water in
cells swell may burst (turgid)
e.g. pure water
Osmosis plant vs animal
Both have phospholipid bilayer
both are partially permable.
Only plant cell has cell wall (cellulose and fully permeable)
Animal cell does not
Osmosis can happen both ways in both types (in and out)
Cell placed in solution with lower water potential:
animal : water leaves through cell surface membrane
vol of cell decreases
cells shrinks
Plant: water leaves through cell surface membrane.
vol of cell decreases.
Protoplast shrinks
cell is plasmolysed
Higher conc:
animal: water enter…
vol inc
no cell wall for pressure
streatched (eventual burst
Plant: same stuff
protoplast expands/ push against cell wall, fully inflated and turgid now.
Where does the energy for active transport come from?
respiration
what is energy required for in active transport?
To make the carrier protien change shape allowing it to transfer ions/molecules across the cell membrane.
What are the uses of active transport?
Reabsorption of useful molecules and ions into the blood after filtration into the kidney.
Absorption of some products of digestion from the digestive tract
loading sugar from the photosynthesising cells of leaves into teh phloem tissue for transport around the plant
loading inorganic ions from the soil into root hairs.
Co-transport definition
coupled movement of substances across a cell membrane via a carrier protien.
Absorption of glucose
Co-transport
Sodium ions and glucose molecules are transported into the epithelial cells via facilitated diffusion
This can only continue if the concentration gradient is maintained.
Active transport of sodium ions out of the cell into the blood maintains this gradient.
The glucose molecules exit the epithelial cells and enter the blood via facilitated diffusion.
Rate of diffusion factors:
Simple:
surface area of exchange surface
concentration gradient across exchange surface
Thickness of exchange surface
Facilitated:
Concentration gradient across exchange surface
number of channel or carrier protiens available in the exchange surface.
Speciallised cells for diffusion
Root hair cells.
specialliesed shape, root hair, increases the surface area so rate of water uptake by osmosis is greater.
(more water and mineral ions)
thinner walls than other plant cells
water can move through easily
permanent vacuole containing cell sap
more concentrated than soil water
high water potential gradient is maintained.
Epithelial cells in small intestine:
microvilli.
increased durface area for greater rate of diffusion
constant blood supply maintains a high concentration gradient between lumen and epithelial cell.
