OCR
A-LEVEL
BIOLOGY
Foundations in Biology
Biological Membranes 1
Time allowed
74 minutes
MARK SCHEME
Score Percentage
/62 %
4.1 | CELL BIOLOGY | QUESTION PAPER 1 1
, Question Expected Answers Marks Additional Guidance
1 (a) Marks can be awarded for an annotated diagram
IGNORE ref to ‘fluid mosaic model’
phospholipid bilayer containing proteins ; ACCEPT glycoprotein / channel protein / carrier protein / etc. for
protein
head / hydrophilic region, facing outwards DO NOT CREDIT ref to hyrophobic heads or hydrophillic tails
OR
tail / hydrophobic region, facing inwards ;
ref to intrinsic and extrinsic (glyco)proteins / ACCEPT transmembrane for intrinsic and on surface for
described ; extrinsic
IGNORE ref to functions such as ‘carrier / channel’ etc.
idea of: glycoproteins / glycolipids, sticking out (of IGNORE glycoproteins / glycolipids are, extrinsic / on the
bilayer / membrane); outside / on surface
cholesterol, inside bilayer / between phospholipids ; 3 max CREDIT between fatty acid tails
(b) (i) Mark the first answer on each prompt line. If the answer is
correct and a further answer is given that is incorrect or
contradicts the correct answer then = 0 marks
active transport / uptake ;
(transport / carrier) protein ; ACCEPT intrinsic protein / transmembrane protein
2 DO NOT CREDIT channel protein / extrinsic protein
(b) (ii) not permeable to, ammonia / NH3 / ammonium / Response must be specific to permeability to ammonia
NH4+ ; CREDIT ammonia cannot pass through membrane
ACCEPT selectively permeable so does not allow passage of
ammonia (into the cells)
IGNORE ‘selectively / partially, permeable’ unqualified
1 IGNORE ‘not permeable to alkalis’
PhysicsAndMathsTutor.com
, Question Expected Answers Marks Additional Guidance
(b) (iii) IGNORE refs to increase in permeability / leaky as the question
asks about structure not properties
phospholipids / (named) molecules, vibrate more /
move around more / have more kinetic energy ;
increases, size / number, of gaps, in membrane / CREDIT creates gaps in membrane
between phospholipids ; ACCEPT holes for gaps
IGNORE ref to pores, ref to gaps created by proteins denaturing
bilayer, becomes more fluid / melts ; IGNORE membrane / phospholipids become more fluid
proteins / glycoproteins, denatured ; ACCEPT description of denaturing e.g. 3D shape / tertiary
structure, changes
IGNORE enzymes denature , ref to active site
max 3
QWC ; max 1 Any two technical terms from the list below used appropriately
and spelled correctly :
phospholipid(s) bilayer
kinetic energy (ref to molecules - do not credit in ref to
membrane or cell)
denature(d) (must refer to proteins or glycoproteins)
4 max
Total 10
PhysicsAndMathsTutor.com
A-LEVEL
BIOLOGY
Foundations in Biology
Biological Membranes 1
Time allowed
74 minutes
MARK SCHEME
Score Percentage
/62 %
4.1 | CELL BIOLOGY | QUESTION PAPER 1 1
, Question Expected Answers Marks Additional Guidance
1 (a) Marks can be awarded for an annotated diagram
IGNORE ref to ‘fluid mosaic model’
phospholipid bilayer containing proteins ; ACCEPT glycoprotein / channel protein / carrier protein / etc. for
protein
head / hydrophilic region, facing outwards DO NOT CREDIT ref to hyrophobic heads or hydrophillic tails
OR
tail / hydrophobic region, facing inwards ;
ref to intrinsic and extrinsic (glyco)proteins / ACCEPT transmembrane for intrinsic and on surface for
described ; extrinsic
IGNORE ref to functions such as ‘carrier / channel’ etc.
idea of: glycoproteins / glycolipids, sticking out (of IGNORE glycoproteins / glycolipids are, extrinsic / on the
bilayer / membrane); outside / on surface
cholesterol, inside bilayer / between phospholipids ; 3 max CREDIT between fatty acid tails
(b) (i) Mark the first answer on each prompt line. If the answer is
correct and a further answer is given that is incorrect or
contradicts the correct answer then = 0 marks
active transport / uptake ;
(transport / carrier) protein ; ACCEPT intrinsic protein / transmembrane protein
2 DO NOT CREDIT channel protein / extrinsic protein
(b) (ii) not permeable to, ammonia / NH3 / ammonium / Response must be specific to permeability to ammonia
NH4+ ; CREDIT ammonia cannot pass through membrane
ACCEPT selectively permeable so does not allow passage of
ammonia (into the cells)
IGNORE ‘selectively / partially, permeable’ unqualified
1 IGNORE ‘not permeable to alkalis’
PhysicsAndMathsTutor.com
, Question Expected Answers Marks Additional Guidance
(b) (iii) IGNORE refs to increase in permeability / leaky as the question
asks about structure not properties
phospholipids / (named) molecules, vibrate more /
move around more / have more kinetic energy ;
increases, size / number, of gaps, in membrane / CREDIT creates gaps in membrane
between phospholipids ; ACCEPT holes for gaps
IGNORE ref to pores, ref to gaps created by proteins denaturing
bilayer, becomes more fluid / melts ; IGNORE membrane / phospholipids become more fluid
proteins / glycoproteins, denatured ; ACCEPT description of denaturing e.g. 3D shape / tertiary
structure, changes
IGNORE enzymes denature , ref to active site
max 3
QWC ; max 1 Any two technical terms from the list below used appropriately
and spelled correctly :
phospholipid(s) bilayer
kinetic energy (ref to molecules - do not credit in ref to
membrane or cell)
denature(d) (must refer to proteins or glycoproteins)
4 max
Total 10
PhysicsAndMathsTutor.com
