Download Answer/Explanatory Notes

WELSH JOINT EDUCATION COMMITTEE
CYD-BWYLLGOR ADDYSG CYMRU
General Certificate of Education
Tystysgrif Addysg Gyffredinol
Advanced Subsidiary/Advanced
Uwch Gyfrannol/Uwch
MARKING SCHEMES
SUMMER 2003
BIOLOGY
INTRODUCTION
The marking schemes which follow were those used by the WJEC for the 2003 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.
ASSESSMENT UNIT BI 1
JUNE 2003
Question
1
Marks
Available
Answer/Explanatory Notes
(a)
Characteristic
Prokaryotic Eukaryotic Plant Cell
Chromosomes
Ribosomes
Membrane organelles
Respiration in mesosomes





4
(b)
comparison needed
Prokaryotic
Eurokaryotic
Size up to 5 m/smaller
Size up to 40 m/larger
Cell wall not of cellulose/
Cell wall of cellulose
of murein
ribosomes smaller
ribosomes larger
(not: plasmids/flagella unless structure described/pili)
1
[5]
2
(a)
amino acid
1
(b)
COOH/carboxyl/carboxylic
1
(c)
NH2/amino/amine
1
(d)
'R' group variable/not fixed
1
(e)
(i)
C – CO – NH – C
H2O
2
(ii)
Condensation
1
(iii)
Peptide
(allow: dipeptide)
1
[8]
3
(a)
(i)
Approximately 20 amino acids
(allow: 20 to 27)
(ii)
some are punctuation/start-stop codons
some are coded more than once/code is degenerate
64 coded in a three base system
(<3/4/16) not enough to code for all amino acids
1
1
2
Question
Answer/Explanatory Notes
(b)
(i)
(ii)
(iii)
4
(a)
(b)
(c)
5
(a)
Methionine, valine, glutamic acid, aspartic acid,
valine, aspartic acid
(one mark for each two correct amino acids)
3
TAC CAA CTT CTA CAA CTG
(one mark for each two correct triplets)
3
Transcription
1
[10]
1 and 3
2 and 4
2
Children one and three have one band from father
Children one and three have one band from mother
Children two and four do not/match completely/are clones
(not: half from father and half from mother; allow
consequential error). Any 2/3.
Police/forensic/identifying criminals/determining new
species/paternity/genetic disease research.
2
1
[5]
(i)
Lipase
1
(ii)
Breaking of a bond (allow: large to small molecules)
Chemical insertion (not: addition)
Of water
2
(iii)
(b)
Marks
Available
(i)
pH reduced/more acidic
Lipid hydrolysed to fatty acids/
(Fatty acids) cause low/acidic pH
1
Start with maximum marks and deduct one at a
time for the following errors:
Incorrect plot
Poorly drawn curve (allow: ruled lines)
Inappropriate scales (insufficient use of graph paper)
Axes not labelled/no units
(ii)
1
Rate remains constant/can't increase
Substrate/lipid occupies active site/at lower
concentrations of lipid not all active sites occupied/
at 0.7% lipid concentration all sites occupied
Extra lipid can't access sites
(not: limiting factor unqualified)
2
3
1
1
Question
Answer/Explanatory Notes
(iii)
6
(a)
(i)
(ii)
(b)
Steeper curve (up to 0.7%)
A = Glycoprotein/carbohydrate/glycocalyx/
polysaccharide
(not: sugars/glycolipid)
B = Phosphate/polar group/hydrophilic head/
phospholipid head
C = Hydrocarbon/non polar tails/hydrophobic
tails/fatty acids (not: tails/lipid layer)
D = Transmembrane protein/carrier protein/
channel protein/intrinsic protein
(not: protein)
E = Protein/extrinsic protein
Fluid mosaic/Singer and Nicholson
(not: mosaic)
Glucose
Polar molecule
Phospholipid layer/hydrophobic region impermeable
Protein channels provide passage
Hydrophilic linings to channels (allow: water filled pores)
Ref. Protein carriers/transporter molecules/transmembrane
protein
Ref. facilitated diffusion
Vitamin A
Non polar
Passes through directly/no channels required
Dissolves in phospholipid layer/hydrophobic regions
Diffusion
(c)
Active transport
Osmosis
Endo/exo/phago/pino-cytosis or description
(not: ref. to diffusion or facilitated diffusion)
Marks
Available
1
[11]
5
1
2
2
2
[12]
7
(a)
Light
1
(b)
X = cilia/brush border
Y = basement membrane
(not: cell/plasma membrane)
2
3
Question
Answer/Explanatory Notes
(c)
(d)
(e)
Cilia move/beat/wave (allow consequential error for 'villi')
Mucus carried along/moved/removed
(not: ref. to goblet cells)
Marks
Available
2
Distance allowed 34-36mm
35
1000
1
35  10-3mm/35m or eq. in nm.
1
Collection/many/(large) number of cells/group (not: layer)
Similar structure
Carrying out a particular function/working together
Any 2/3.
2
[9]
8
(a)
A
Follows interphase
B
During which replication/copying/doubling of
DNA/chromosomes occurs
C
Prophase, metaphase, anaphase, telophase, (correct
order anywhere in answer)
D
Chromosomes shorten/thicken/condense
E
Appear as two chromatids
F
Joined at centromere
(not: joined together/pair off/just on diagram)
G
Centrioles migrate to opposite poles in animal cells
(not: centrioles divide)
H
Aster formation/spindle fibres span cell/run from
pole to pole/spindle formed
I
Nuclear envelope/membrane/nucleolus, disappears
J
Chromatids line up at equator/metaphase plate
4
Question
Marks
Available
Answer/Explanatory Notes
(b)
K
Centromeres attached to spindle fibres
L
Centromeres split
M
Chromatids/chromosomes drawn apart/to (opposite)
poles
N
By shortening/contraction of spindle fibres
O
Chromosomes uncoil/lengthen
P
Nuclear envelope/membrane formed
(allow: annotated diagrams)
(reference to chromosomes instead of chromatids
penalised once only then consequential error;
action in wrong phase penalised)
A
Insulin producing
identified
B
Ref. restriction enzymes/endonucleases
C
Production of cDNA/description
D
Ref. reverse transcriptase
E
Plasmids/vector extracted/obtained from bacterial
cells
F
Ref. E. coli
G
Contain marker gene/antibiotic resistance gene/
DNA or marker gene inserted
H
Plasmid cut by same restriction enzyme
I
Insulin gene mixed with (cut) plasmid
5
gene/mRNA
cut/isolated/
[10]
Question
Answer/Explanatory Notes
J
Complementary/antiparallel
K
Bonding/base pairing
L
Ref. Sticky ends
M
Ref. to Ligase (seals/anneals)
N
Forms recombinant DNA
O
Added to bacterial culture
P
Bacteria taking up recombinant DNA identified by
use of antibiotic
Q
These cells cloned/replicated/cultured/allowed to
grow/multiply
6
Marks
Available
10
ASSESSMENT UNIT BI 2
JUNE 2003
Question
1
Answer/Explanatory Notes
(a)
(b)
(c)
(d)
decreases
Marks
Available
1
ribs move/inspiration
1
capillaries
1
number of deaths/(1000) of population/year
1
(e)
pyramid with broad base and narrow tip;
producer, primary consumer, secondary consumer
1
1
(f)
pollution with nitrate ions/increase in water temp/fertilizers
(not: eutrophication/nutrient levels)
1
(g)
omnivore - meat and plant eater
carnivore - meat eater ONLY
1
1
[9]
2
(a)
(i)
the volume/amount of air breathed in and out in one
breath
(not: ref. to oxygen/breathing rate)
1
(ii)
correct label of vital capacity
1
(iii)
correct calculation of vital capacity = 5.0 - 1.5 = 3.5;
dm3 (not: litres)
1
1
(iv)
to absorb/remove carbon dioxide
(not: detect/test levels)
1
(v)
(to prevent) volume changes/expansion due to
temperature
1
(b)
diffusion
1
(c)
asthma - bronchi constrict/inflamed (not: smaller); alveoli
unaffected; rate reduced/slower (not: low/slow)
emphysema - bronchi unaffected; aveoli coalesce/accept
drawing; rate reduced/lower
6
[13]
7
Question
3
Answer/Explanatory Notes
(a)
(b)
(c)
biconcave disc (not: doughnut/disc shaped); increasing in
surface area/diffusion rate/can fold to fit through capillaries
contains haemoglobin; aids oxygen transport
no nucleus/organelles - more (space) for haemoglobin
(not: more oxygen) (Any 4)
(Function must relate to adaptation)
4
(a)
4
(i)
maintains carrying capacity OR appropriate figures/
no change
1
(ii)
blood can carry (nearly) as much oxygen despite
drop in available oxygen.
1
(iii)
exercise/respiration rate
(not: ref. to CO2)
1
(iv)
enables more oxygen to be unloaded;
for a (small) drop in pO2 or converse
1
1
(i)
curve drawn to left of original (max. 100, through
origin, labelled)
because Llamas live at higher altitude; with less
available oxygen/oxygen deficient atmosphere
(Any 1)
1
(ii)
(d)
Marks
Available
In red blood cells;
CO2 combines with H2O to give hydrogen carbonate ion/
carbonic acid;
which combines with Na in plasma to give sodium
hydrogen carbonate;
chloride shift allows movement of C1  into red blood cell;
therefore maintaining electrochemical neutrality
(2 max) (not: balancing charge or pH)
1
2
[13]
(i)
root hair
1
(ii)
active transport/uptake
(not: facilitated diffusion)
1
(iii)
symplast route
1
(iv)
stops apoplast pathway/ water containing ions freely
diffusing through cell walls;
enables active transport/facilitated diffusion through
cell membrane;
(allow: selective absorption, not: selectively
permeable)
8
2
Question
Answer/Explanatory Notes
(b)
(c)
(i)&(ii) curled leaf; sunken stomata; hairy stomata; thick
cuticle; fewer stomata; more hairs on leaf
(Any 2)
K ions pumped in (requiring ATP)/starch converted to
malate;
decrease water potential of cells/increase solute potential;
water drawn in by osmosis/follows concentration gradient;
guard cells become turgid;
uneven thickening of Guard cells; push cells apart
(3 max)
Marks
Available
2
3
[10]
5
(a)
X - ammonia/ammonium
1
Y - nitrate/NO3+
1
(b)
nitrogen fixed/converted (into ammonium);
by (symbiotic)/free living bacteria in soil/root nodules
1
1
(c)
de-nitrification/leaching/crop removal/harvest/deforestation
(not: burning/monocrop)
1
(d)
build-up of dead organisms/excretory products and faeces/
lack of decomposition qualified
leads to a reduction in ammonium/soil nitrate/soil fertility
(not: nitrogen/nutrients/ref. to carbon cycle)
1
1
(e)
increased drainage/increased aeration/air in soil/nitrifying
bacteria use aerobic respiration/more nitrites/reduction in
anaerobes
(not: refs. to mixing nutrients)
1
[8]
6
(a)
The sequence of alteration of communities in time
(EQ)/example/development of climax community
(b)
Less distance for seeds to travel to Krakatoa;
Greater diversity on neighbouring tropical islands;
ref. warmer climate.
(Any 2)
(c)
(d)
Death of plants; provide (humus in) developing soil;
breakdown of plant materials leads to nitrogen compounds/
nutrients;
humus retains water
(Any 2)
increase in number of niches/shelter/habitat;
increase in available food/variety of food
1
2
2
1
1
[7]
9
Question
7
Answer/Explanatory Notes
Marks
Available
Heart Question
Cardiac cycle
A
Atria contract forcing blood into ventricles
B
through atrio-ventricular valves or correctly named
C
Ventricles contract & blood forced out of heart into (aorta &
Pulmonary) artery/arteries
D
Through semilunar valves/pulmonary and aortic valves;
E
ref. Closing of A-V or semilunar valves correctly related to
pressure; (i.e. comparative pressure)
F
Heart/Cardiac muscle is myogenic/ external stimulus not
needed to initiate contraction (allow: heart)
G
SA node control contraction rate (or rhythm) of muscle cells;
(NOT initiate)/acts as pacemaker
H
Wave of contraction/excitation spreads over atria and atria
contract simultaneously/ together
I
AV node transmits impulses to ventricles;
J
ref. only route for impulse/delay/ Purkinje fibres/bundle of
His;
K
Wave of contraction spreads over ventricles & ventricles
contract simultaneously:
(7 max)
7
10
Question
Answer/Explanatory Notes
Marks
Available
X2 circulation
L
ref. separation of blood supply to pulmonary/lungs and
systemic/body pathways; (actual terms not needed) or
description/diagram
M
Sustains high blood pressure in systemic/RA for pulmonary
N
Circulation is faster in systemic/RA for pulmonary
O
oxygenated/deoxygenated blood kept separate
P
improved oxygen distribution/efficiency
Q
sustains higher metabolic rate for organism
(3 max)
3
[10]
11
Question
7
Answer/Explanatory Notes
Marks
Available
Pest Control Question
Comparative
i.e. ref. to both needed, statements together.
Z
Comparative description of two methods/integrated control
A
Chemical is cheap and biological expensive
B
Chemical kills all insect life, biological is specific/allows
pollinators to return
C
Organisms can develop resistance to chemical but not to
biological
(Any 3)
3
Chemical
D
fast in action
E
localised effect
F
affects food chains/can't eat crop
G
pest can reappear
Y
environmental damage
Biological
H
long term effect
I
can spread/escape if not controlled/more suitable for closed
environment, e.g. greenhouses
J
no residues that affect food chains/less environmental damage
K
detailed knowledge of life cycle required
L
pest level reduced to economically accepted level/RA
M
risk of control becoming "super pest"
Example
N
Encarsia/control of white fly/ladybirds/cane toads
O
Pyrethroids
(Any 7)
[10]
12
AS/ADVANCED MODULE BI 4
June 2003
Question
Marks
Available
Answer/Explanatory Notes
1
Causative organism
Disease
Bacterium
Cholera

Protoctistan
Virus
1

Malaria

Influenza
Salmonellosis
1

1
1

Smallpox
1
One mark per correct tick
[5]
2
(a)
(b)
(i)
Adenosine triphosphate/ATP
1
(ii)
A Phosphate (groups)
B Adenine/nitrogenous/(organic) base
C Ribose/5C/pentose sugar
1
1
1
active transport or example e.g. Na/K pump (not: uptake of
glucose unqualified);
muscle contraction (not: movement/activity);
protein synthesis/synthesis of materials within cells;
nerve transmission;
cell division (not: growth)
(Any 2)
(c)
oxidative phosphorylation (is the breakdown of
glucose/eq) using oxygen/aerobically to release ATP (in
respiration)/add phosphate to ADP
photophosphorylation is the synthesis of ATP using light/in the
light stage (of photosynthesis).
2
1
1
[8]
13
Question
3
Answer/Explanatory Notes
Marks
Available
Before
1
2
3
Mention of (natural) barrier e.g. prevents entry of pathogens/
sebum prevents skin 'cracking'
Natural skin/flora/eq preventing growth of many pathogens
Mention of skin pH preventing growth of pathogens
(Any 2)
2
After
1
3
4
5
Phagocytosis/bacteria engulfed (not eaten) by phagocytes/ white
blood cells/neutrophils;
2
Inflammation/swelling/increase blood supply bringing
WBCs/eq and nutrients;
Mast cells production of histamine
Blood clotting/scab formation to seal wound
Local raised temperature reduces bacterial growth
(Any 3) (not: ref. to production of antibodies/blood flow flushes
out wound)
3
[5]
4
(a)
(i)
(ii)
(iii)
Rennin/prorennin/
Pepsin/pepsinogen
1
trypsin/trypsinogen (not: endo/exopeptidase)
1
Bile/pancreatic juice/intestinal/eq juice passes into duodenum/gut;
which contains alkaline (salts)/bicarbonate.
1
1
(b)
C is involved in digestion;
D is involved in absorption (not: absorption of water).
1
1
(c)
(i)
1
1000
(ii)
antibiotic gene may transfer to pathogenic/disease
causing /harmful bacteria;
1
[8]
14
Question
5
(a)
(b)
(c)
Answer/Explanatory Notes
Marks
Available
36 colonies from 0.1cm3 of 103 dilution;
360 from 1.0cm3 of 103 dilution;
360x103/3.6x105 bacteria in original culture
3
E;
E shows the lowest number of colonies of any of the samples at all
dilutions/E is the only concentration showing no bacterial growth
at 103 dilution/quoted examples/lowest count at highest dilution.
2
102;
103;
Both of these give a range of countable plates/101 gives too many
uncountable plates and 104 gives too few countable plates.
3
[8]
6
(a)
A clear Y shaped molecule
(b)
(i)
(c)
1
A
substance/polysaccharide/recognition
site/protein/
foreign/non-self molecule which causes the production
of/reacts with antibodies/immune system
(not: chemical/chemical marker/molecule)
1
(ii)
it will divide/clone continuously i.e. continue to grow
(not: quickly/is a clone)
1
(iii)
hybrid/hybridoma
1
pregnancy testing kits;
anticancer drugs/cancer treatment (magic bullets in context)/drug
targetting;
treatment of infections e.g. rabies/tetanus (allow: disease
qualified);
disease diagnosis;
transplant surgery/blocking T lymphocyte activity
separation of chemicals from a mixture.
(Any 2)
2
[6]
15
Question
7
(a)
Answer/Explanatory Notes
(i)
A
B
(ii)
(b)
Marks
Available
light
harvesting
unit/complex/centre/antenna
complex/accessory pigments (not: antenna/light
harvesting/ primary pigment)
1
reaction centre/trap/chlorophyll a
1
chlorophyll (a);
chlorophyll (b);
carotene;
xanthophyll.
(Any 2)
2
(iii)
thylakoid/granal membranes/intergranal membrane;
inside chloroplasts
1
1
(i)
oxygen is a (by-)product of photosynthesis;
the rate of oxygen production;
will be proportional to the rate of photosynthesis/more
photosynthesis more oxygen produced.
(Any 2) (not: ref. to amounts)
2
(ii)
carbon dioxide levels will fall in the tube-replace after
each experiment/add CO2 source;
temperature will vary-needs a thermostatic water
bath/constant temperature/screen;
Filter not accurate for wavelength, need to check.
(Any 2) (allow: inaccuracy unqualified if clear from
correction)
(not: ref. to counting bubbles/pH)
2
(iii)
one large peak in the blue region;
one smaller peak in the red region.
no size difference - one mark only
1
1
(iv)
action spectrum
1
[13]
16
Question
8
(a)
Answer/Explanatory Notes
Athletes have a higher rate of oxygen consumption (at all
levels)/converse/athletes have a maximum oxygen consumption
which is much higher (25% higher) than non-athletes;
There is only an increase of 1 from 1200 to 1400 J min 1 kg 1 /
max oxygen consumption is reached at 1400 J min 1 kg 1 /max
58, 45.
alternatively:
Non athletes have a lower overall increase in oxygen
consumption over the range of energy expenditures (or
figs)/converse;
Marks
Available
1
1
Max oxygen consumption is reached at 1200 J min 1 kg 1 ;
(i.e. comparison needed)
in athletes higher lung capacity;
better circulatory system/heart capacity;
greater number of mitochondria;
in non-athletes accept converse
(Any 1) (not: more (developed) muscles)
(b)
(c)
As exercise increases non-athletes produce more lactate than
athletes.
Athletes have no lactate until 1200 J min 1 kg 1
max figure of 305 mg min 1 kg 1
non-athletes have lactate appearing at 1000 mg min 1 kg 1
(much higher) figure of 590 mg min 1 kg 1
Any 2
in athletes more oxygen available so there is less anaerobic
respiration/converse
(i)
(ii)
(d)
1
2
1
It is deaminated (in the liver);
the amino group is converted to urea;
and excreted;
the residue is converted to acetyl CoA/ pyruvate/Krebs
cycle intermediates;
and oxidised in the respiratory pathway.
(Any 3)
3
liver
1
reduced NAD/NADH2
oxidised NAD/NAD
1
Carbon dioxide/CO2
Ethanol/alcohol
1
[12]
17
Question
9
(a)
Marks
Available
Answer/Explanatory Notes
ATP Synthesis Mark Scheme
Similarities
a
Both need high energy electrons
b
Both need stalked particles/ATP synthetase
c
Both need proton pumps
d
Both involve a series of carriers/pumps in electron transport
chain
e
Both need protons which are pumped into a cavity
f
Both
are
involved
in
creating
an
chemiosmotic/H-ion/H+/proton gradient
g
Both involve redox reactions
18
electrochemical/
Question
Answer/Explanatory Notes
Marks
Available
Differences
h
Cristae/(folded) inner membrane carries stalked particles in
mitochondria Or Intermembrane cavity in mitochondria/
diagram
i
Thylakoid membrane in chloroplasts carries stalked
particles Or Thylakoid cavity in chloroplasts/diagram
j
3 (types of) proton pumps in mitochondria
k
1 (type of) proton pump in chloroplasts
l
Water formed during ATP synthesis in mitochondria/
Protons derived from glucose breakdown
m
Water broken down (in non-cyclic photophosphorylation) in
chloroplasts/protons derived from water/photolysis produces
H ions
n
High energy electrons are derived from chlorophyll in
chloroplasts
o
High energy electrons are derived from glucose/reduced
[10]
NAD/FAD in mitochondria
9 maximum if no comparison
19
Question
(b)
Marks
Available
Answer/Explanatory Notes
Vaccination essay Mark Scheme
a
Involves using non-pathogenic/non disease causing forms or
products of the microorganism
b
To stimulate an immune response
c
Which confers protection against subsequent infection/build
up resistance
d
Any example from weakened/attenuated virus/bacteria
killed virus/bacteria
neutralised toxin/separated antigen
e
One disease example e.g. rubella/German measles/tetanus/
smallpox/flu/MMR/diphtheria/polio/any valid vaccination
f
B lymphocytes/plasma cells are stimulated to produce Ab/Ag
stimulates 1 response
g
And memory cells (which remain inactive)
h
If the pathogen/Ag enters the body memory cells recognise
the Ag
i
(Clones of) cells produce the Ab immediately
j
These destroy the pathogen/Ag before the person is ill/causes
a 2º (immune) response
k
Some
stable
pathogens/diseases/smallpox
have
been
eliminated worldwide
l
Influenza virus/malaria organism mutates and cannot be
eliminated by vaccination
m
Travel increases infection spread/droplet infection is difficult
to control/viruses have no effective curative treatment/animal
reservoirs/unvaccinated boys/people act as a source of
infection
n
Reports of possible side effects reduces take-up of
vaccination of children/leads to an increased number of cases
o
Public information/education and identification of contra
indication in individual cases minimises risks
20
ASSESSMENT UNIT BI5
JUNE 2003
Question
1
Answer/Explanatory Notes
(a)
Marks
Available
(i)
anti-diuretic (hormone) / ADH
1
(ii)
human chorionic gonadotrophin / HCG
1
(iii)
oxytocin
1
(b)
actin and myosin
1
(c)
amplifies the vibration of the ear drum /sound (waves) /
transmits vibration from the ear drum to the inner ear
(Any 1)
1
maintains genetic uniformity / multiplying hybrid plants /
multiplying plants that won't breed true / breeding plants
that are hard to reproduce naturally / quicker as no need
for pollination and seed production / larger numbers
produced from a single plant / cost effective / easy to
transport and store / recovery of endangered plants / no
plant disease as healthy stock selected and sterile
conditions used / no seasonal restrictions on germination.
Cheaper or quicker must be qualified. (Any 1)
1
(d)
(e)
(f)
bans on trade in ivory / bans on whaling / restrictions on
trade in furs / restriction on sale of exotic birds /
conservation of whole environment (e.g. 'Operation
Tiger') / breeding programmes between zoos / botanic
gardens / establishment of seed banks / any suitable
example that clearly shows international co-operation.
(Any 1) (not: name of organisation unqualified)
(allow: national parks qualified/fishing - implies
international)
geographical isolation / named geographical feature /
habitat change / differences in behavioural mechanisms /
differences in breeding mechanisms / changes in
morphology.
(not: volcano/earthquake)
1
1
[8]
21
Question
2
Answer/Explanatory Notes
Marks
Available
1
(a)
form / variant / alternative form of a gene
(b)
(i)
Parental genotypes
Possible gametes
(ii)
Parental genotypes
Possible gametes
F1 genotypes
F1 phenotypes
(allow: superscripts,
letters unless key)
(iii)
SSrr
1
(i)
XeO / XeY
(superscript 'e' must attach to X); O or Y needed)
1
(ii)
XeXe
1
(iii)
XEXE;
XEXe.
1
1
(c)
(d)
Rr

R and r
rr.
Rr;
(2);
SG

GG;
S and G
G(G);
SG (SG)
GG (GG);
silvery grey
grey.
not: lower case G / other
different base (sequence) in gene / allele (not: DNA)
different triplet code; sequence of codons
different (sequence) of amino acids;
different protein / enzyme / polypeptide
(Any 3)
1
1
1
1
1
1
1
3
[16]
3
(a)
(b)
hydrolysis digestion / breakdown by enzymes of reserves
/ endosperm (not: breakdown unqualified)
starch converted to sugars / glucose / named
respiration / loss of carbon dioxide;
sugars used by / sent to growing regions / embryo; (not:
embryo uses energy store from endosperm);
increase as first leaves produced
photosynthesis.
(Any 4)
(i)
(ii)
(c)
4
amylase / enzyme / carbohydrase
from the seed;
converts starch to maltose;
hydrolysis / digestion;
(Any 3) (not: breakdown)
3
less amylase / enzyme produced in absence of
embryo
1
cotyledons
(allow: seed leaf,not: dicotyledon)
1
[9]
22
Question
4
Answer/Explanatory Notes
Marks
Available
(a)
mitosis
(b)
(i)
Fusarium
1
(ii)
banana plants genetically identical / clones;
same susceptibility / lack of resistance to Panama
disease;
no / little mutation;
close planting.
(Any 3)
3
natural selection;
fungicide is selective agent / selective pressure;
variation between individuals;
chance / random mutation;
some individuals have selective advantage / better
chance of surviving;
survival of resistants / death of non-resistants (not:
survival of the fittest);
mutation / ability to survive pesticide passed on to
offspring;
increased allele frequency.
(Any 5)
5
(c)
(d)
(i)
(ii)
1
normally achieved with breeding programmes;
(using) reservoir of genes / alleles;
bananas are sterile / seedless / reproduce
asexually;
no easy way to incorporate new genes / alleles.
(Any 2)
genetic engineering / induced mutation / gene
splicing / inserting a (resistant) gene.
2
1
[13]
23
Question
5
Answer/Explanatory Notes
(a)
A
germinal epithelium / germ cells;
B
mitosis to produce spermatogonia;
(not: multiplication)
C
growth to produce primary spermatocyte;
D
meiosis I to produce secondary spermatocyte;
E
meiosis II to produce spermatid;
F
maturation / spermiogenesis / differentiation to
produce spermatozoa;
G
role of Sertoli cells - nutritive or protection;
H
digestion / softening of corona radiata / zona
pellucida;
I
acrosome reaction or description;
J
penetration of head into secondary oocyte;
K
fertilisation membrane to prevent polyspermy;
L
stimulates meiosis II;
Marks
Available
M fusion of nuclei to form zygote;
(Any 9)
N
9
Accurate spelling not detracting from understanding
grammar, logical account.
(i.e. ease of reading)
1
[10]
24
Question
5
Answer/Explanatory Notes
(b)
A
inside about -60 to -70mV (compared with outside);
B
maintained by sodium (-potassium) pump;
C
[K+] higher inside / [Na+] higher outside;
D
membrane more permeable to K+ which diffuse /
leak / move out;
E
all or nothing / threshold value;
F
action potential occurs when membrane becomes
more permeable to Na+ and they flood in / sodium
gates;
G
depolarisation;
H
inside about +40mV (compared with outside);
I
K+ then diffuse / move out and repolarise the
membrane;
refractory period explained;
J
K
local currents stimulate next part of neurilemma /
membrane / axon;
L
myelin sheath increases distance over which local
currents can act to bring about depolarisation or
speeds up transmission by jumping from node to
node;
Marks
Available
M depolarisation only at nodes of Ranvier;
(Any 9)
N
9
Accurate spelling not detracting from understanding
grammar, logical account.
(i.e. ease of reading)
1
[10]
25
Question
6
Answer/Explanatory Notes
(a)
(b)
(c)
(d)
(e)
Marks
Available
somewhere to live / housing;
logging / wood products;
development / industry / roads;
fuel.
mining / drilling
(Any 2) (allow: construction once only)
2
provides fertile, material / soil / acts as a fertiliser;
good crop, growth / yield;
no need to buy fertilisers;
remove pests.
(Any 2)
2
less fertile soil;
less material to burn;
less (plant) has grown during fallow period;
less (fertile) ash;
less time for soil to regain fertility;
crops remove nutrients.
(Any 2)
2
food crop and rubber crop / two crops;
cash crop / income;
land can be felled in (about) same time;
sustainability.
(Any 2)
2
(i)
assume candidate is referring to plantation, unless
otherwise stated
far fewer species / very little diversity;
only 2 plant types / trees and herbaceous plants;
no (2 of) climbers, epiphytes, shrubs;
ref. figures (comparative) / 360 vs 10 species.
(Any 2)
(ii)
2
assume candidate is referring to agroforest,
unless otherwise stated
all types represented in both
fewer tree species;
fewer epiphyte / shrub species;
more herbaceous species;
(approx.) same number of species of climbers;
fewer species / less diversity;
ref. figures (comparative) / 360 vs 260 species
(Any 3)
26
3
Question
Answer/Explanatory Notes
(f)
Marks
Available
depends upon agriculture;
plantations seem to be destructive;
reduced / do not permit species diversity / monoculture;
agroforestry allows forest to regenerate;
maintains a (fairly) high level of diversity;
(Any 2)
2
[15]
7
(a)
(b)
(i)
water;
or
osmosis;
salt / Na+/Cl-;
diffusion;
or urea;
diffusion.
(ii)
too large to pass through (pores in) membrane
(not: tubes)
(iii)
concentration gradient maintained;
continual replacement / flow of dialysis fluid;
continual circulation of blood;
waste products / impurities / excess water
removed from blood more effectively;
(Any 3)
(i)
(ii)
large surface area / thin membrane so short
diffusion distance;
dialysis fluid needs to be in close contact with
blood (capillaries);
so that substances can pass from blood into
dialysis fluid.
dialysis fluid not continually replaced;
concentration gradient not maintained;
(once some movement of substances from blood
has taken place) equilibrium is reached;
less efficient removal of substances from blood.
(Any 2)
(iii)
increase solute / glucose / salt concentration /
more negative water potential.
(iv)
less efficient;
further distance for substances to diffuse / slower
diffusion.
27
2
1
3
2
2
1
2
Question
(c)
Answer/Explanatory Notes
Marks
Available
(i)
they are genetically identical / clones
(not: similar)
1
(ii)
(brother and sister because . . .)
have common genetic ancestry / husband and wife
are not related genetically / brother and sister have
genes / DNA from same parents.
(iii)
(cells of) new kidney recognised as foreign / not
identical to those of recipient;
(cells of new kidney have) antigens
T killer (lymphocytes) cause lysis of target cells /
destroy kidney;
helper T cells are activated;
B lymphocytes / plasma cells;
produce antibodies.
(Any 4)
1
4
[19]
GCE Biology/MS/(June 2003)/AOB
01 August 2003
28
Welsh Joint Education Committee
245 Western Avenue
Cardiff. CF5 2YX
Tel. No. 029 2026 5000
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E-mail: [email protected]
website: www.wjec.co.uk/exams.html