MS3
£3.00
WELSH JOINT EDUCATION COMMITTEE
CYD-BWYLLGOR ADDYSG CYMRU
General Certificate of Education
Tystysgrif Addysg Gyffredinol
Advanced Subsidiary/Advanced
Uwch Gyfrannol/Uwch
MARKING SCHEMES
SUMMER 2005
BIOLOGY
INTRODUCTION
The marking schemes which follow were those used by the WJEC for the Summer 2005
examination in GCE Biology. They were finalised after detailed discussion at examiners'
conferences by all the examiners involved in the assessment. The conferences were held
shortly after the papers were taken so that reference could be made to the full range of
candidates' responses, with photocopied scripts forming the basis of discussion. The aim of
the conferences was to ensure that the marking schemes were interpreted and applied in the
same way by all examiners.
It is hoped that this information will be of assistance to centres but it is recognised at the
same time that, without the benefit of participation in the examiners' conferences, teachers
may have different views on certain matters of detail or interpretation.
The WJEC regrets that it cannot enter into any discussion or correspondence about these
marking schemes.
BIOLOGY
ASSESSMENT UNIT BI1
Question
1.
Answer/Explanatory Notes
Marks
Available
Ribosome mark scheme
(i)
1 mark for decent diagram showing 2 clear subunits
1 mark for any label
large subunit
small subunit
groove which mRNA fits into
tRNA binding site
2
(ii)
RNA/Ribosomal RNA
Protein
(not: amino acids/nucleic acid)
1
1
(iii)
(rough) endoplasmic reticulum
1
(iv)
protein/polypeptide synthesis
1
(v)
nucleolus/nucleolus and cytoplasm
(not: nucleus/cytoplasm)
1
Total 7 marks
1
Question
2.
Answer/Explanatory Notes
Marks
Available
Lipid mark scheme
(i)
Triglyceride
Phospholipid
Structural
difference 1
3 fatty acids
2 fatty acids
Structural
difference 2
(Glycerol head only)
Glycerol + phosphate
head
(not: phosphorus)
Where compound
is found in
organisms
Under
skin/subcutaneous/
blubber
Around body organs
Fur/feathers
Nerve cells
Smooth
ER/golgi/vesicles
seeds
chloroplasts
Cell/plasma
membranes
(not: hydrophilic/hydrophobic/polar/non-polar/fat unqualified)
One mark
per row = 3
(ii)
Stearic/Saturated has more H or converse.
Stearic has no double bonds (in hydrocarbon chain/double
C-C bonds) or converse.
Stearic acid is a straight hydrocarbon chain/not kinked/bent
or converse.
1
(iii)
Stearic acid/saturated (fatty acid).
1
Total 5 marks
2
Question
3.
Answer/Explanatory Notes
Marks
Available
Genetic fingerprinting Q mark scheme
(a)
(b)
(c)
(i)
Genetic/DNA fingerprinting/DNA profiling.
1
(ii)
blood/saliva/skin/hair/semen any 2
(not: fingerprints/body fluids/urine/sweat)
1
(iii)
suspect 2
1
(iv)
it is the only one which has the banding pattern which
exactly matches the one at the scene of the crime.
(allow: samples are the same)
1
(i)
Used to cut the DNA (into sections.)
(not: genes)
1
(ii)
Separation of DNA fragments.
1
Paternity suits/eq
1
Total 7 marks
3
Question
4.
Answer/Explanatory Notes
Marks
Available
Cell division mark scheme
(a)
Correct ID of LS root zone of cell division.
(not: cross in vascular bundle/across all diagram)
Correct ID of TS anther zone of cell division.
(allow: to top of root cap but not in root cap)
2
Root labelled MITOSIS (correct spelling only).
Anther labelled MEIOSIS (correct spelling only).
(b)
2
Correct drawings as below.
(number must be consistent)
3
On equator
As bivalent, labelled.
deleted)
(c)
(Allow: at right angles if poles
Correct label for centriole, drawn.
Centromere
Bivalent
One mark each
3
Total 10 marks
4
Question
5.
Answer/Explanatory Notes
Marks
Available
Beetroot Q mark scheme
(i)
{very little increase/0-7 units} up to {40ºC/first 4
temperatures;
rapid rise at 50ºC/rise from 7 to 80 at 50ºC;
small rise from 80 to 100 units from 50 to 70ºC.
higher temperature, darker solution/higher reading
(ii)
2
Membrane (proteins) are stable between 10 and 40ºC/at low
temperatures;
(Appearance of the red pigment means that) the (tonoplast
and) cell membrane has been damaged between 40 and 50ºC/
at high temperatures;
(meaning) pigment has leaked out of cells/sap vacuole/
change in membrane permeability/damaged membrane;
proteins change shape/denature and come out of bilayer;
phospholipids bilayer has become too fluid/cannot retain
proteins.
(iii)
3
Dissolves phospholipids/destroys cell membrane structure;
(So) pigment leaks out.
(not: ref. to higher or lower readings)
1
Total 6 marks
5
Question
6.
Answer/Explanatory Notes
Marks
Available
DNA Q mark scheme
(a)
(i)
A DNA
B RNA
1
(ii)
Ribose (not: pentose)
1
(iii)
Nucleus/nucleolus/mitochondria/chloroplasts
1
(iv)
Hydrogen
1
(v)
RNA/B is a short molecule, DNA/A is a long
molecule;
Pentose in DNA contains one less oxygen.
RNA/B is much shorter than DNA/A;
A is helix, B is straight molecule/not helix.
(b)
Uracil replaces thymine in RNA/B.
(not: DNA has deoxyribose and RNA has ribose)
1
(i)
A bond/base pairs with T and C with G.
1
(ii)
Any suitable figure from table indicating
A approx = T/C approx = G
(data and species)
1
Purines.
1
(iii)
Total 8 marks
6
Question
7.
Answer/Explanatory Notes
Marks
Available
Immobilised enzyme mark scheme
(a)
(i)
(ii)
2(mm)
(because) it gives the highest percentage of product
(not: converse)
1
smaller beads give a larger total area (exposed to the
milk/substrate);
(not: smaller beads have large surface area)
or
smaller beads will pack more closely (so there is more
enzyme:subtrate);
the milk will have longer contact/flow more slowly
around small, close packed beads;
or
gives more time for the enzyme and subtrate to come
into contact.
(iii)
(iv)
2
Percentage product would increase/get more product;
More time for enzyme-substrate complexes to occur/
for reaction.
1
temperature/milk type/source (not: pH)
1
(b)
glucose and galactose
1
(c)
Can tolerate/more stable
condition/temps/pH qualified;
in
a
wider
range
of
Product not contaminated with enzyme/pure product/easily
reused qualified;
Several enzymes (requiring different conditions) may be
used together;
Enzymes easily added/removed = more control.
(allow: ref. to continuous production qualified,
not: ref. to cost)
2
Total 8 marks
7
Question
8.
Answer/Explanatory Notes
Marks
Available
Cystic fibrosis mark scheme
(a)
protein/capsid
nucleic acid/DNA/RNA
2
(b)
gene therapy
1
(c)
Use of liposomes;
Transfer of non CF gene (into plasmid);
Coated in (spheres of) phospholipids/lipid (bilayer);
Breathed into lung via aerosol/inhaler.
(d)
3
Gets into nucleus;
Insertion into genome/chromosome;
Transcription/eq; (in context)
Translation/eq. (in context)
(e)
2
Activation of oncogenes;
Unexpected disease caused/leukaemia;
Allergic response.
(not: side effects unqualified)
1
Total 9 marks
8
Question
9. (a)
Answer/Explanatory Notes
Enzyme essay mark scheme
a
Biological catalysts/speed up a chemical reaction
(not: catalyst unqualified)
b
By lowering activation energy/labelled diagram
c
Globular protein/labelled diagram/tertiary structure or eq.
d
With active site/specific shape
e
Into which substrate(s) fits and is converted to product(s)
f
Correct reference to lock and key/induced fit or suitably
labelled diagrams
PH
g
Enzymes have a narrow optimum pH range
h
Large deviations from this optimum may result in
denaturation/shape change
i
Small pH changes cause reversible changes (which may
inactivate the enzyme)
Temp
j
Rate of reaction increases with increasing temperature
k
Because of increased number of collisions of active site and
substrate
l
Enzymes are denatured by higher temperatures above 45C
Optimum for most (mammalian) enzymes approx 37C
m
At low temperatures enzymes are inactive/eq
Inhibitors
n
Description of the 2 types of inhibitors competitive
p
Non-competitive/labelled diagrams
q
Correct egs cyanide for non-comp, malonic acid for comp
Must mention pH, temp and inhibitors to get 10 marks. If one or
more missing Max. 9 marks.
9
Marks
Available
Question
9. (b)
Answer/Explanatory Notes
Marks
Available
DNA replication/transcription essay mark scheme
DNA replication
a
DNA replication has to occur prior to cell division/during
interphase
b
(Parental) DNA helix unwinds (has to be clear that this is all
the DNA, not just a section)
c
Complementary strands separate due to breaking of (weak)
H-bonds (could be given in transcription)
d
Base pairing (AT, CG) occurs between the bases of the both
template strands and free nucleotides
e
DNA polymerase separates the 2 DNA strands/joining of
DNA nucleotides
f
Produces pair of identical helices/strands
g
Semi-conservative replication/one new chain, one original
h
Mention of Meselson and Stahl expt/correct details of
experiment
Transcription
i
Occurs during protein synthesis
j
Base sequence of a (cistron) gene is converted to mRNA
(not: DNA is converted)
k
Gene (only)/short section (eq) unwinds
l
RNA polymerase
nucleotides
c
DNA unzips/c from replication if not already given
m
One strand acts as a template
n
Free RNA nucleotides align themselves opposite the
complementary base/mention of uracil instead of thymine,
uracil pairs with adenine
p
Complete mRNA peels off and exits (nucleus) through a
nuclear pore/DNA zips back up
attaches
to
the
DNA/joins
RNA
Total 10 marks
10
ASSESSMENT UNIT BI 2
Question
1.
Answers/Explanatory Notes
Marks
Available
(a)
diaphragm;
1
(b)
diffusion;
1
(c)
emphysema;
1
(d)
asthma;
1
(e)
tidal;
1
[5]
2.
(a)
1:1;
2
0.75:1/3:4/1:1.3;
(b)
ratio of surface area to volume large;
diffusion sufficient to meet requirements/shorter diffusion
path;
oxygen for respiration/removal of carbon dioxide;
as cells/organisms become larger, surface area to volume
ratio smaller;
diffusion can't supply oxygen/nutrients/remove carbon
dioxide;
3 max
(comparison needed)
[5]
11
Question
3.
(a)
Answers/Explanatory Notes
(i)
(ii)
21060 x 100;
1,700,000
1.24(%);
Marks
Available
2
reflected;
passes straight through the leaf/transmission through leaf
(not: transmission unqualified)
misses photosynthetic parts/leaves;
wrong wavelength;
3 max
absorbed by water;
not present because of season;
(b)
(c)
(d)
(e)
(i)
4;
1
(ii)
energy at last/4th trophic level only 21 units;
insufficient to pass on/support another level;
2
death/decay;
excretion/urine;
faeces/egestion;
2 max
bacteria;
fungi/saprophytes;
2
producer floats out/removed from, ecosystem/fishing/
migration qualified;
1
[13]
12
Question
4.
(a)
Answers/Explanatory Notes
Marks
Available
nutrient content /three named nutrients decreases;
named example plus figures from table;
lack of leaves/trees to decompose;
less nutrients released into soil;
increased leaching;
no trees to hold soil/reduce run off of water;
3 max
(Any figures quoted require units)
(b)
increased daytime soil temperature (after clearing);
rate of respiration/enzyme activity of decomposers
increases;
2
[5]
13
Question
5.
Answers/Explanatory Notes
(a)
Marks
Available
arteries have thicker walls;
arteries have more muscle in walls;
(not: veins have no muscle)
more elastic in walls;
veins have valves;
3 max
arteries have smaller lumen;
(accept reverse points)
(b)
(i)
artery;
1
(ii)
5  0.5kPa;
1
(iii)
contraction of ventricle/ventricular systole;
1
(iv)
ventricle relaxes/diastole;
1
(v)
further away from heart;
friction/more resistance;
increased cross sectional area of vessels;
(c)
(i)
2 max
separate systemic/body;
and pulmonary/lungs systems;
blood passes through heart twice during one complete
circuit
(ii)
2 max
blood contained in vessels;
1
[12[
14
Question
6.
(a)
Answers/Explanatory Notes
(i)
Marks
Available
stomata open earlier/close later/open longer, on a sunny
day;
lighter earlier/later/longer;
stomata open wider/aperture increases on a sunny day;
more/higher light intensity;
rate of opening/closing greater on a sunny day;
higher light intensity/more light;
(ii)
(b)
4 max
excessive transpiration/too much water lost/plant tries to
conserve water/prevents wilting;
1
(i)
xerophytes;
1
(ii)
feature
explanation
feature
explanation
(iii)
long root;
large surface area for absorption/reaches
down to water deposits;
(not: ref. to anchorage)
few/small leaves/foliage close to ground;
less transpiration/reduce water loss;
thick cuticle;
sunken stomata;
rolled leaves;
hairs on leaves; (not: hairs unqualified)
leaves reduced to spines;
water storage organs
2
2
2 max
[12]
15
Question
7.
(a)
Answers/Explanatory Notes
Marks
Available
(i)
E;
1
(ii)
C-D;
1
(b)
decreases;
blood enters/forced into aorta;
(forced) out of ventricle;
(c)
(i)
point where the two lines diverge;
(ii)
pressure falls in ventricle;
2 max
1
below that in aorta;
blood tries to flow back;
forces valves to close;
(d)
2 max
sino atrial node;
(not: SAN)
1
[8]
16
Question
8.
(a)
Answers/Explanatory Notes
(i)
A
loading of sucrose;
B
into sieve tube cells/at source
C
by active transport/ATP/energy dependent;
D
sucrose lowers water potential (of sieve tube cell);
E
water moves down water potential gradient;
F
by osmosis;
G
(high) hydrostatic pressure generated;
H
sucrose unloaded/removed at sinks/roots;
I
used for respiration/storage/converted to starch;
J
water passes out of sieve tube cell;
K
low hydrostatic pressure at sink/root;
L
pressure gradient from source to sink/along sieve tube;
M water plus dissolved substances/sucrose/assimilates
flow down gradient;
(ii)
N
ref to bidirectional flow;
O
ref to no apparent role for sieve plates/companion
cells;
P
ref to different rates of movement;
Q
cytoplasmic streaming observed;
Marks
Available
8 max
2 max
(Incorrect use of 'glucose' penalised once)
[10]
17
Question
(b)
Answers/Explanatory Notes
A
birth rate and death rate;
B
population grows if birth rate higher; (ORA)
C
immigration and emigration;
D
population grows if immigration exceeds emigration;
(ORA)
E
increased predation decreases population;
F
disease will reduce size of a population;
G
effect of weather/temperature qualified;
H
availability of food qualified;
I
availability of living space qualified;
J
human involvement/intervention;
K
specific example of human involvement;
L
ref. density dependent/ factors;
Marks
Available
M ref. to carrying capacity;
N
labelled diagram/description of a growth curve (3 of 4
phases needed);
O
ref. to some factors can cause a population to crash;
18
10
ASSESSMENT UNIT BI 4
Question
1.
(a)
(b)
Answers/Explanatory Notes
Marks
Available
(i)
chloroplasts
1
(ii)
dehydrogenases
1
(iii)
lacteal
1
(iv)
inflammation
1
(i)
endemic present but a low/constant level in population/
area,
1
epidemic spreading to larger number in population/same
area
(ii)
bacteriostatic stops bacteria growing/multiplying/reproducing
bactericidal kills bacteria
1
[6]
2.
(a)
(b)
(c)
(i)
to prevent overheating / remove heat generated by process
1
(ii)
to maintain optimum / constant pH
1
(iii)
to prevent contamination with unwanted microbes
(not: purifying air)
1
contains nitrogen;
1
microbe needs nitrogen to synthesise proteins/nucleic acids
1
Penicilliun produces penicillin during stationary phase
1
Resources become scarce during overcrowding (in
stationary phase) / ref. to competition/secondary metabolite
1
[7]
19
Question
3.
Answers/Explanatory Notes
(a)
(b)
Marks
Available
B circled on drawing
1
(i)
Temperature (kept at 37ºC) / pH (2) / level of acidity
1
(ii)
no microbes / sterile / denature proteases or enzymes in
beef
1
in stomach churning / mechanical digestion / separates
fibres
1
presents large surface area (for enzyme to act upon) / more
ES complexes
1
(c)
continuous enzyme production
(not: ref. to HCl)
(d)
(i)
(ii)
(iii)
1.
trypsin(ogen) / chymo~
(not: peptidases)
1
2.
pancreas
1
gut wall / organs made of protein / secreting cells
1
active enzyme would digest wall / organ / cells / prevents
autolysis
(not: cell wall)
1
removal of amino group/excess cannot be stored / ref. to
urea
1
so that remainder of molecule may be stored / utilised /
converted to carbohydrate.
1
[12]
20
Question
4.
(a)
Answers/Explanatory Notes
(i)
(ii)
(b)
Marks
Available
A
glycolysis
1
C
Krebs / citric acid cycle
1
D
electron transfer / respiratory chain
(not: ETC/ TCA / electron transfer)
1
P
carbon dioxide
1
Q
ethanol / alcohol
1
R
oxygen
1
S
water
1
(iii)
NAD / nicotinamide adenine dinucleotide / NADH2
1
(i)
use energy from the electrons
1
to pump protons into intermembrane space / across
membrane
1
(ii)
R  S (allow: Oxygen to water)
1
(ii)
it takes up / removes hydrogen / protons / forms water
1
(iv)
protons flow down gradient / diffusion;
1
through (a channel in) ATP synthetase / ATPase / stalked
particles;
1
the energy is used to make ATP (from ADP).
1
[15]
21
Question
5.
(a)
(b)
Answers/Explanatory Notes
Marks
Available
(i)
oxygen
1
(ii)
27 mm / 2.7 cm (allow: consequential error)
1
(iii)
40.69 mm3 – no units 1 mark only (allow: 40.5 to 40.7)
81.3 to 81.5
2
(i)
collect bubbles of gas (over a fixed time period) (use
syringe to move bubble) and measure its length / volume;
1
insert coloured filters (between lamp and pondweed) and
repeat
(not: different colours)
1
steps to avoid stray light / temperature change; max 3
(c)
(i)
(at low light intensities) increasing light intensity increases
rate / volume of gas produced;
1
at higher light intensities / quoting values increasing light
intensity does not affect rate.
(not: ref. to time/levels off)
1
(ii)
0.9 to 0.4m
1
(iii)
the temperature / carbon dioxide level / volume NaHCO3
1
(iv)
when a process is affected by more than one factor or
description
1
the overall rate is limited by that factor which is closet to
its minimum value.
(not: factor in least supply)
(i.e. within not between factors)
1
[13]
22
Question
6.
(a)
(b)
(c)
(d)
Answers/Explanatory Notes
Marks
Available
(i)
spherical / round
1
(ii)
coccus
1
(i)
(cell wall) contains peptidoglycan / murein / glycoprotein
1
do not have outer layers with / have little lipoprotein /
lipopolysaccharide
1
(ii)
cell wall / cross links in the wall
1
(iii)
don't have (cell) wall
(not: no metabolic pathways)
1
(i)
A, D and F (must get all 3)
1
(ii)
which are methicillins
1
(iii)
E
1
cover skin lesions / sores with (clean, dry) dressings
1
don't share towels / bed linen with family / friends
prevent direct physical contact / stay in quarantine
1
wash hands before touching objects others might use
1
tell others to wash hands after touching you / your
dressings / objects you might have contaminated; Any 3
(not: stay away from infected person / multiples of same
suggestion)
[12]
23
Question
7.
(a)
Answers/Explanatory Notes
Marks
Available
A
energy source is (a photon) of light, pigments /
chlorophyll absorb light energy / light energy changed
to chemical energy
1
B
pigments include chlorophyll a and b, carotene and
xanthophylls
1
C
to absorb different wavelengths / parts of spectrum
1
D
reference to antennae complex / photosystems
(embedded in (thylakoid) membranes)
1
E
energy transferred between pigment molecules and to
reaction centre (chlorophyll)
1
F
emission of electrons by reaction centre (chlorophyll) /
P700 / photosystems
1
G
electron acceptors
1
H
electron transfer chain (between PSII and PSI)
1
I
reference to proton pumps ATPase / chemiosmosis
1
J
electrons (emitted from PS II) replaced from water –
photolysis / correct description of photolysis
1
K
photolysis takes place inside thylakoid space /
mopping up of protons in stroma by NADP
1
L
therefore contributes to electrochemical gradient
1
M NADP is reduced / NADPH2 end product or final
electron acceptor
1
N
reference to cyclic phosphorylation
1
O
Energy is stored in the form of ATP
1
Maximum 10 marks from available 15.
[10]
24
Question
7.
(b)
Answers/Explanatory Notes
Marks
Available
A
humoral response involves production of proteins
(globulins) called antibodies
1
B
they are specific to the antigen
1
C
antibodies are Y shaped / formed from 4 polypeptide
chains
1
D
the antibody antigen complex inactivates the antigen
1
E
an example of how / identifying for phagocytosis /
agglutination / lysis / immobilisation / neutralisation
1
F
humoral response involves (lymphoid tissue to form)
B lymphocytes / B cells
1
G
each B cell (or T cell) has receptors for its specific
antigen
1
H
antigen stimulates proliferation of plasma cells and
memory cells
1
I
memory cells remain ready to divide if same antigen is
encountered again (i.e. increase number rather than
output)
1
J
cell mediated response involves T lymphocytes / T
cells
1
K
T cells develop / mature in thymus gland
1
L
there are 3 types of T cell/ref. To killer cells, helper
cells and memory or suppressor cells
1
M function of killer cells, directly kill pathogen/
bacterium cell infected by virus
1
N
function of helper cells, stimulate phagocytosis / make
T or B cells competent / assist killer cells
1
O
role for suppressor cells - suppress B cells /
lymphocyte action after infection / switch off immune
system when antigen not present
Maximum 10 marks from available 15.
[10]
All points may be awarded for a suitably annotated diagram, but marking points must be
explicit.
25
ASSESSMENT UNIT BI 5
SECTION A
Question
1.
Answers/Explanatory Notes
(a)
2, 5, 4, 7, 6, 1, 3
(b)
Protoctista;
Marks
Available
[1]
Fungi;
[4]
Animalia;
Plantae;
(c)
Cell Wall of murein / not cellulose;
(not: chitin)
No nuclear membrane/nucleus;
Circular DNA;
DNA not associated with histones;
[Max 3]
No membrane bound cell organelles /mitochondria/
chloroplasts etc.;
Small ribosomes/70S ribosomes
(not: large)
No meiosis;
Plasmids
(d)
Offspring infertile
[1]
26
Question
2.
(a)
Answers/Explanatory Notes
Marks
Available
(i)
Both alleles express themselves.
[1]
(ii)
Form of a gene/ref. to same locus
[1]
(iii)
Parental genotypes: C C
LL;
Gamete
L;
C
F1 genotypes: all C L
F1 phenotypes: all Chevron with pale patch;
(F1 genotypes and phenotypes 1 mark)
Gametes: C
L
F2 genotypes: CC
CL
C
L;
CL
LL
F2 phenotypes chevron chevron with pale patch
pale patch;
(F2 phenotypes and genotypes 1 mark)
[1]
[1]
Ratio 1 : 2 : 1
(b)
Accept other symbols if key given.
Accept gametes if on Punnett square.
[5]
(i)
Continuous
[1]
(ii)
Tall
[1]
(iii)
Tt x Tt
Parental genotype
[1]
Gametes;
TT
Tt
Tt
tt
Genotype offspring
3 tall l:1 Dwarf
(Both for 1 mark)
(c)
(d)
Ratio; (allow: 75%, 25%)
(i)
9:3:3:1
[1]
(ii)
1:1:1:1
[1]
Named characteristic;
Named environmental factor.
(not: examples of selection)
[1]
[1]
27
Question
3.
Answers/Explanatory Notes
(a)
Marks
Available
A = glomerulus/malpighian corpuscle;
B = Bowman's capsule;
C = proximal/first convoluted/coiled tubule A. PCT;
D = Loop of Henle, A. descending limb;
(b)
(i)
(ii)
E = collecting duct;
[5]
The longer the loop of Henle the lower the water potential
of the urine/more concentrated urine/solute potential
higher.
[1]
Sodium (ions) pumped out; of ascending limb;
creates a region of low water potential around collecting
ducts;
water moves out of collecting duct/descending limb;
by Osmosis;
ref. counter current.
(c)
[Max 3]
(i)
Hypothalmus (1); brain (1); osmoreceptors. Any 2.
[2]
(ii)
(posterior) pituitary;
[1]
(iii)
first/proximal convoluted tubule;
[1]
(iv)
(distal convoluted tubule) collecting ducts.
[1]
28
Question
4.
(a)
Answers/Explanatory Notes
(i)
(ii)
Mutation;
Marks
Available
[1]
Selective advantage (if Warfarin being used);
(not: just ref. to natural selection and survival of the fittest)
more resistant rats survived;
formed breeding population;
Max. 3
passed on beneficial allele to offspring/more resistant
alleles in gene pool.
(iii)
(Sexual) reproduction/interbreeding;
[2]
migration.
(b)
If Warfarin not used there is no selective advantage/
description; Disadvantage rats with allele need large
amounts of vitamin K; therefore selected against/die out.
2 from 3
(not: more rats survive therefore greater selection pressure)
29
[2]
Question
5.
Answers/Explanatory Notes
(a)
A.
Fibre, Myofibril.
B.
Sarcolemma,
sarcoplasm,
large
numbers
mitochondria, SR.
T tubules, multinucleate,
nuclei. 3 from.
C.
Sarcomere qual.
D.
Tin Actin/Thick Myosin
E.
Ref. Z line. Correct position.
F.
Ref. A band. Myosin
G.
Ref I band actin only.
H.
Ref. H zone.
I.
Ref. M line.
Max. 5
J.
Sliding.
K.
evidence for sliding.
L.
Cross bridges.
M.
Myosin head binds to actin.
N.
Details of ratchet mechanism.
O
Function of ATP. Breaks bond between actin and
myosin. Ref. SR.
P
Role of Calcium. Change of shape of tropomyosin
exposing binding site
Max. 5
30
Marks
Available
Question
Answers/Explanatory Notes
(b)
A.
Pollen tube growth controlled by tube nucleus.
(A Diag)
B.
Generative nucleus.
C.
Mitosis.
D.
2 male gametes/nuclei.
E.
Embryo sac A ref. 8 nuclei.
F.
Micropyle, ref. pollen tube entry.
G.
Double fertilisation.
H.
One male gamete fuses with egg cell nucleus.
I.
To produce a zygote.
J.
One male gamete fuses with polar nuclei.
K.
To produce primary endosperm nucleus/triploid
cell.
L.
Develops into endosperm
M.
Integuments become testa.
N.
Zygote becomes embryo.
O
(cotyledons) plumule and radicle.
P.
Ovule becomes seed.
31
Marks
Available
Question
6.
Answers/Explanatory Notes
(a)
(b)
(c)
(i)
(ii)
(d)
(e)
Genetically identical; from small groups of cells/
meristems/explants/individual cells; artificial medium/agar
[3]
No nucleus/mitosis cannot take place/differentiated cells.
[1]
Genetically identical; grow at same rate; look same; same
size; same flavour; preserves favoured alleles or converse.
Genetically same (if not above); no resistance because no
variation; no variation to survive climate change owtte;
reduction in gene pool; high cost or difficulties in
production.
(not: cost unqualified)
(i)
Chromosome.
(ii)
Break down of spindle fibres, during mitosis/nondisjunction/increased DNA replication/chromatids don't
separate.
(iii)
Marks
Available
[Max 2]
[Max 2]
[1]
Pairing of homologous chromosome cannot take place; no
meiosis; no gametes/haploid cells produced
[Max 1]
[Max 2]
Reversion of virus to disease causing form;
Virus could be changed into different form;
Bacteria/virus could be toxic to humans or insects;
Virus/bacterium could transfer to another species;
Accept ref. ethical reasons qualified e.g. Why change
colour of leaves when there is no nutritional value?
Accept ref. increase cost of plants putting financial burden
on farmers;
Accept other valid points e.g. unknown future side effects.
(not: playing God/genes escaping)
32
[Max. 3]
Question
7.
Answers/Explanatory Notes
(a)
(b)
Marks
Available
E.g. of intracellular, described e.g. named respiratory
(allow: digestive if stated as lysosomal)
[1]
E.g. of extracellular, described e.g. named digestive
[1]
DNA, code for primary structure/amino acid sequence.
Ribosomes, translation/joining a. acids together/site of
protein synthesis.
Golgi body, assembly and packaging/modify proteins.
Lysosomes, contain (proteolytic) enzymes;
Exocytosis,
membrane.
(c)
(i)
release/export
of
enzymes
across
cell
[5]
Competitive (similar shape to substrate), binds to active
site;
[2]
Non-competitive binds to enzyme but not at active site;
(not: ref. to non-reversible/reversible)
(ii)
(iii)
Competitive, (reversible) inhibitor; binds to active sites in
enzyme; prevents ethylene glycol entering; slows
production of oxalic acid/less acid produced; can leave
active site.
[Max. 4]
Enzymes work at optimum pH/specific pH;
Changes secondary/tertiary structure of enzyme;
Affects H bonds/ionic bonds/disulphide bridges;
Active sites destroyed/distorted;
Shape of enzyme changes/configuration;
Slight pH change causes inactivation/extreme causes
denaturation.
33
[Max. 4]
Question
(d)
Answers/Explanatory Notes
Marks
Available
Enzymes always proteins/hormones proteins or steroids;
Hormones produced by endocrine glands/ductless glands;
Hormones transported in blood to site of action;
Enzymes often work inside cell in which produced,
hormones target cells;
Enzymes more lower activation energy;
Ref. speed of action;
Enzymes more susceptible to pH/temp changes
(not: ref. active site/hormones homeostatic and enzymes
catalysts)
(comparative statements not necessary)
GCE Biology Markscheme (June 2005)/HJ
34
[Max. 2]
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