cell membranes

Question 1

describe the fluid mosaic model of membranes

Answer 1

fluid: phospholipid bilayer in which individual phospholipids can move = membrane as flexible shape
mosaic: extrinsic and intrinsic proteins of different sizes and shapes are embedded

Question 2

explain the role of cholesterol and glycolipids in membranes

Answer 2

cholesterol: steroid molecule in some plasma membranes : connects phospholipids and reduces fluidity to make bilayer more stable
glycolipids: cell signalling and cell recognition

Question 3

explain the functions of extrinsic and transmembrane proteins in membranes

Answer 3

~binding sites/ receptors
~antigens
~bind cells together
~involved in cell signalling

Question 4

explain the function of intrinsic transmembrane proteins in membranes

Answer 4

~electron carriers
~channel proteins
~carrier proteins

Question 5

explain the function of membranes within cells

Answer 5

~provide internal transport systems
~compartmentalisation
~provide reaction surface
~selectively permeable to regulate passage of molecules in and out

Question 6

explain the functions of the cell-surface membrane

Answer 6

~involved in cell signalling/ cell recognition
~selectively permeable to regulate transport of substances
~isolates cytoplasm from extracellular environment

Question 7

name and explain 3 factors that affect membrane permeability

Answer 7

~use of solvent may dissolve membrane
~PH changes tertiary structure of membrane proteins
~temperature high temp denatures membrane proteins

Question 8

outline how colorimetry could be used to investigate membrane permeability

Answer 8

~use plant tissue with soluble pigment in vacuole. tonoplast and cell surface membrane disrupted= increased permeability= pigment diffuses into solution
~select colorimeter filter with complementary colour
~use distilled water to set colorimeter to 0
~measure absorbance/ % transmission value of solution
~high absorbance / low transmission = more pigment in solution

Question 9

define osmosis

Answer 9

water diffuses across semi-permeable membranes from an area of higher water potential to an area of lower water potential until a dynamin equilibrium is established

Question 10

what is water potential

Answer 10

~pressure created by water molecules measured in kPA
~distilled water has water potential of 0
~more soluble= water potential more negative

Question 11

how osmosis affect plant and animal cells

Answer 11

~into cell
- plant: protoplast swells -turgid
-animal:lysis
~out cell
-plant: protoplast shrinks = cell flaccid
-animal : crenation

Question 12

define simple diffusion

Answer 12

~passive process that requires no ATP
~net movement of small lipid soluble molecules down concentration gradient

Question 13

define facilitated diffusion

Answer 13

~passive process
~specific channel or carrier proteins with complementary binding sites transport large and or polar molecules down concentration gradient

Question 14

explain how channel and carrier proteins work

Answer 14

channel: hydrophilic channels bind to specific ions = one side of protein opens and the other closes
carrier: binds to complementary molecule = conformational change releases molecule on other side of membrane

Question 15

define active transport

Answer 15

active process moves molecules against conc gradient
~ATP hydrolysis releases phosphate group that binds to carrier protein, causing it to change shape

Question 16

define exocytosis and endocytosis

Answer 16

~active process
~involved in bulk transport & transporting large particles
~vesicles fuse with cell surface phospholipid membrane

Question 17

name 5 factors that affect rate of diffusion

Answer 17

~temperature
~diffusion distance
~surface area
~size of molecule
~difference in concentrations (how steep is gradient)