Biological membranes are like the vigilant guards of cells, separating the inside from the outside world. Picture them as dynamic barriers, selectively letting in essential molecules while keeping out the rest.
This exam paper will really test your boundaries just like it did mine.
MARK SCHEME ...
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
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