NOTES: Italics indicates NOT from the mark scheme (often means no
mark schemes relating to the spec point). These are taken instead
from the CIE A Level textbook, which occasionally includes extra
detail to help my own understanding. All others are directly copied
from CIE 9700 mark schemes.
Mark scheme abbreviations: I = ignore, A = accept, R = reject. A
semi-colon “;” separates marking points, which are sometimes
numbered. “AVP” = any valid point. See the start of any mark
scheme for full abbreviations.
4. Cell membranes and transport
Fluid mosaic:
1 phospholipid bilayer ;
2 fatty acid core / fatty acid tails orientated inwards ;
3 protein ; e.g. integral and peripheral proteins, proteins scattered (in
phospholipid bilayer)
4 proteins and phospholipids, can move around (in phospholipid
bilayer)
5 ref. to hydrophobic / hydrophilic, regions on, phospholipid / protein
6 cholesterol between phospholipid molecules, heads at the
membrane surfaces
Roles of molecules in membranes:
Phospholipids:
1 ref. to hydrophilic / polar, phosphate, head / group and hydrophobic
/ non polar, hydrocarbon / fatty acid, tails / chains ;
2 ref. to forms part of a bilayer ;
3 (fatty acid) tails / chains, may be saturated or unsaturated ;
heads:
4 form hydrogen bonds with water/ interacts with water/AW ;
5 stabilise the membrane ;
tails/chains:
6 idea that unsaturated fatty acids contribute to fluidity (of
membrane) ;
mark schemes relating to the spec point). These are taken instead
from the CIE A Level textbook, which occasionally includes extra
detail to help my own understanding. All others are directly copied
from CIE 9700 mark schemes.
Mark scheme abbreviations: I = ignore, A = accept, R = reject. A
semi-colon “;” separates marking points, which are sometimes
numbered. “AVP” = any valid point. See the start of any mark
scheme for full abbreviations.
4. Cell membranes and transport
Fluid mosaic:
1 phospholipid bilayer ;
2 fatty acid core / fatty acid tails orientated inwards ;
3 protein ; e.g. integral and peripheral proteins, proteins scattered (in
phospholipid bilayer)
4 proteins and phospholipids, can move around (in phospholipid
bilayer)
5 ref. to hydrophobic / hydrophilic, regions on, phospholipid / protein
6 cholesterol between phospholipid molecules, heads at the
membrane surfaces
Roles of molecules in membranes:
Phospholipids:
1 ref. to hydrophilic / polar, phosphate, head / group and hydrophobic
/ non polar, hydrocarbon / fatty acid, tails / chains ;
2 ref. to forms part of a bilayer ;
3 (fatty acid) tails / chains, may be saturated or unsaturated ;
heads:
4 form hydrogen bonds with water/ interacts with water/AW ;
5 stabilise the membrane ;
tails/chains:
6 idea that unsaturated fatty acids contribute to fluidity (of
membrane) ;
