MS3
/WELSH JOINT EDUCATION COMMITTEE
/£3.00 / CYD-BWYLLGOR ADDYSG CYMRU
General Certificate of Education Tystysgrif Addysg Gyffredinol
Advanced Subsidiary/Advanced Uwch Gyfrannol/Uwch
MARKING SCHEMES
SUMMER 2004
BIOLOGY
INTRODUCTION
The marking schemes which follow were those used by the WJEC for the 2004 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
JUNE 2004
Question Answer/Explanatory Notes Marks
Available
Protein / DNA / Disaccharide / Phospholipid1 / Carbon + Hydrogen + Oxygen / / / / / / / /
Nitrogen + Sulphur / / / X / X / X
Disulphide bonds / / / X / X / X
Glycosidic bonds / X / X / / / X
Peptide bonds / / / X / X / X
Ester bonds / X / X / X / /
1 mark per line [6]
2 (a) G = triose/glyceraldehydes 1
F = amylose 1
C = maltose 1
A = cellulose 1
D = alpha glucose 1
(b) Insoluble (therefore do not affect osmotic potential)/coiled or compact/
glucose easily released or easily added or broken down easily
(Any 2) 2
(c) Benedicts/boil/shows reducing sugar/brick red (precipitate)
(allow: green/yellow)
non-reducing sugar negative/stays blue in above/(heat with) acid/
neutralise/then gives positive with Benedicts
2 points for 1 mark 3
(not: hydrolyse) [10]
3 (a) Thymine 1
Cytosine 1
Adenine 1
Guanine 1
(b) (i) X = Nucleotide 1
(ii) phosphoric acid/phosphate 1
organic base/nitrogenous base/cytosine 1
pentose (sugar)/Deoxyribose/5C sugar 1
(not: Pi/base/purine or pyrimidine)
(c) Z = Hydrogen bond 1
(d) deoxyribose and phosphate/deoxyribose and (nitrogenous) base
or named/pair of entities e.g. amino acids/sugars
(Any 1) 1
Question Answer/Explanatory Notes Marks
Available
(e) uracil/ribose/single strand/shorter/lower molecular weight/transcription
occurring
(Any 2) 2
[12]
4 (a) hydrophilic/polar/phosphate head
hydrophobic/non polar/fatty acid tail
phospholipid
intrinsic protein/protein pore or other correct (not: protein unqualified)
extrinsic protein/carrier protein
glycoprotein/glycolipid
bilayer/drawn
cholesterol
glycocalyx/carbohydrate/polysaccharide
1 mark each if shown in correct position, max 5 if bilayer not shown 6
(b) Fluid: phospholipids/molecules constantly moving/proteins move 1
Mosaic: proteins do not form a continuous layer/patchy or scattered 1
proteins/random pattern of proteins
(c) Hydrophilic heads take up/attract aqueous 'stain',
(hydrophobic tails repel stain) 1
(d) Nucleus
mitochondria
chloroplast
(two correct 1 mark, three correct 2 marks) 2
[11]
5 (a) Meiosis 1
(b) A F B G D E H C [I]
all 8 = 3 marks, 6 = 2 marks, 4 = 1 mark 3
(c) (DNA) replication/pairing of homologous chromosomes/bivalent
formation (not: crossing over/DNA duplication) 1
(d) independent assortment/random assortment
crossing over
random fusion gametes/chromosome numbers halved
mutation
(Any 3) 3
(e) metaphase takes twice as long/longer 1
[9]
Question Answer/Explanatory Notes Marks
Available
6 (a) Competitive inhibitor
similar shape as substrate/binds to/enters active site/
prevents normal substrate binding (not: competes) 2
Non competitive inhibitor
binds to enzyme but not at active site/distorts/denature active site 2
(not: denaturation (of enzyme))
End product inhibition
product of enzyme controlled reaction/
binds to enzyme (slowing down its own production)/
negative feedback 2
(not: ref. to binding to active site)
(b) A and B
(kinetic) energy increases or molecules move faster 1
enzyme and substrate meet more frequently/more enzyme -
substrate complexes formed/
collision rate increases 1
C and D
3D/globular/tertiary structure of protein affected/hydrogen bonds or equivalent
breaking down/active sites break down/denatured 2
(not: enzyme denatured unqualified)
(c) To prevent damage to active sites/prevent enzyme being denatured;
enzymes/proteins would need to be constantly replaced;
accept to give some leeway. 2
(i.e. idea of 'comfort zone' e.g. temperature fluctuation (1)
consequences e.g. denaturation and replacement (1)
[12]
Question Answer/Explanatory Notes Marks
Available
7 (a) A. diffusion with example
B. down concentration gradient/from high to low concentration
C. no energy required/passive
D. facilitated diffusion (plus example)/cotransport and example
E. qualification of facilitated diffusion/cotransport e.g. carriers, faster,
no energy (2 from 3)
F. active transport (with example)/diagram
G. qualification - energy, against concentration gradient, carriers
(2 from 3)
H. osmosis water only
I. definition - high ® low water potential/concentration, SPM
J. correct use of water terminology
L. water potential qualified, accept equation/turgor pressure/
YP opposes inward flow
M. phagocytosis/endocytosis qual
N. pinocytosis qual
O. exocytosis/vesicles qual
P. material injected bacteriophage
[10]
Question Answer/Explanatory Notes Marks
Available
(b) A. alginate beads, gel membrane, adsorbed onto nylon/inert
support
(not: inert casing)
B. reuse of enzymes/easily separated
C. stable - temperature/pH
D. advantage of using enzymes, e.g. not poisonous therefore do not need
to be removed, heat stops action, no contamination of product.
E. rapid.
F. accurate/specific.
G. detect/sensitive to low concentrations.
H. glucose oxidase or any other e.g. monitoring blood sugar, pectinase
I. transduction, converted into electrical output/electronic
current/colour change.
J. restriction enzyme.
K. separation of different size fragments.
L. electrophoresis.
M. probes, dyes, markers, radioactive tracers
N. unique pattern of bands/unique DNA fingerprint for individual
(not: genetic fingerprint)
O. use of technique, e.g. criminal investigation, paternity, defining closeness of evolutionary links, identification.
6 marks for A-I
4 marks for J-O 10
[10]
BIOLOGY
ASSESSMENT UNIT BI 2
JUNE 2004
Question / Answers/Explanatory Notes / MarksAvailable
1 (a) / succession / 1
(b) / spirometer / 1
(c) / emphysema / 1
(d) / autotroph/producer / 1
(e) / sino-atrial node / 1
(not: abbreviation/pacemaker)
[5]
2 (a) / an organism that feeds off another organism
of a different species/host
harms host/doesn't kill host (not: cause disease)
(Any 2) / 2
(b) / quick acting/cheap/localised use/more efficient/effective/ easy to apply/produce
(Any 1) / 1
(c) (i) / chemicals non-specific
(chemicals) would kill wasp
long residual effect on Encarsia
waste of money
(Any 2) / 2
(ii) / cooler climate;
wasp can't fly/little flying below 18°C
would not fly to/reach more slowly, other infected plants in field
whitefly would not be killed/crops remain infected
(not: fly away) (Any 2) / 2
(iii) / honeydew sticky wasps can't move/fly / 1
(d) / can't achieve this/biological control maintains low levels/specific to whitefly / 1
[9]
Question / Answers/Explanatory Notes / Marks
Available
3 (a) / correct axes and labels
appropriate scale (over half of paper used)
correct plot
well drawn curve / 4
(b) / correct figure from graph (150 x 105 ® 130 x 105)
(unit needed but consequential error in e) / 1
(c) / 690 ´ 105 cells / 1
(d) / no/reduced levels of nutrients/increased competition (not: competition)
accumulation of toxins
number of dying equals numbers produced
(not: resources/space/oxygen/food) (Any 2) / 2
(e) / lag phase
log phase/exponential phase / 2
(f) / (steep) decline in curve/death phase
decrease/decline/numbers drop / 1
[11]
4 (a) / Vein
thin wall/little muscle in wall/large (volume) lumen
low pressure blood/large volume blood returning to heart
valve/prevents backflow of blood / 2
Capillary
thin wall/endothelium/wall one cell thick
exchange of materials/formation of tissue fluid/short distance for diffusion / 2
Artery
thick wall/muscle/elastic tissue
high pressure blood (not: to pump blood) / 2
(b) / valve/pocket valve
(not: if valve given in table or specific valves) / 1
[7]
Question / Answers/Explanatory Notes / Marks
Available
5 (a) (i) / denitrification / 1
(ii) / bacteria/fungi/saprophytes / 1
(b) / combined with products of photosynthesis
to form amino acids
to form proteins
growth of new cells/tissues
to form nucleic acids
(Any 3) / 3
(c) (i) / nitrite concentration increases then decreases
use of figures (amount and days)
nitrate concentration increases
after increase in nitrate concentration
use of figures (amount and days)
(Any 3) / 3
(ii) / excretion/waste produced by goldfish/decayed (surplus) fish food / 1
(iii) / converted/oxidised
to nitrite
by bacteria
(Any 2) / 2
(iv) / nitrite converted to nitrate/
nitrate not converted into other products/no plants to absorb nitrates
(Any 1) / 1
(v) / water changed/partially changed/water added/tank cleaned/
vigorous plant growth/new plants put into tank/algal bloom / 1
[13]
Question / Answers/Explanatory Notes / Marks
Available
6 (a) (i) / Leaf B
thicker cuticle
sunken stoma/(deep) air chamber / 2
(ii) / reduced loss through epidermis/cuticle (not: prevents)
traps water vapour/reduces diffusion gradient / 2
(iii) / hairs
traps water vapour
curled leaf
traps water vapour
stomata open at night
vapour can't escape during hot part of day
leaves reduced to spines/leaf area reduced
less surface area/fewer stomata
(Any 2) / 2
(b) (i) / xeromorph/xerophytic / 1
(ii) / low (environmental) temperature
(high) humidity (not: damp)
decrease in/low wind speed
dark day/low light intensity
(Any 2) / 2
[9]
7 (a) / sucrose
(not: sugar(s)/water) / 1
(b) / 14C at top of stem/14C in roots / 1
but absorbed at leaf halfway up stem / 1
(c) (i) / growing point/growth
active process/ATP required/energy required
respiration
carbohydrate in respiratory substrate
(Any 2) / 2
(ii) / sinks; / 1
[6]
Question / Answers/Explanatory Notes / Marks
Available
8 (a) / A unicellular organisms use diffusion
B multicellular organisms are large
C metabolically more active
D substances need to travel distances/around the body
E diffusion only efficient over short distance/too great for diffusion
F diffusion too slow
H ref. surface area to volume ratio being too small in multicellular organisms
I for uptake of nutrients/named nutrient
J oxygen
K removal of waste products
L carbon dioxide/urea
M system/lungs/gills required to distribute/absorb substance/named substance
N quickly
O in sufficient quantities due to large surface area
P so processes/named processes operate efficiently
Maximum 10 marks / 10
Question / Answers/Explanatory Notes / Marks
Available
(b) / A enters root hair
B by osmosis
C water potential of root hair increases/becomes higher than surrounding cells
D water moves into these cells
E movement via symplast/symplasm/cytoplasm to cytoplasm
F via plasmodesmata
G via vacuolar pathway, vacuole to vacuole
H down a water potential gradient
I across cortex/cortical cells
J via apoplast pathway/apoplasm, along cell walls
K until endodermis
L casparian strip prevents movement of water
M redirected into symplasm
N water moves up in root xylem
O reduces water potential in xylem of root
P water enters xylem (from surrounding cells)
Q active transport of salts into xylem
Maximum 10 marks / 10
[10]
BIOLOGY
ASSESSMENT UNIT BI4
JUNE 2004
Question Answer/Explanatory Notes Marks
Available
1. (a) (i) palisade (mesophyll) 1
(ii) Calvin cycle/light independent stage/dark stage 1
(iii) Ribulosebi(s)phosphate/RuBP 1
(b) to absorb light (energy)/act as a transducer/convert light energy into
chemical energy/high energy electrons/harvest or trap light 1
(c) absorption spectrum: the (quantity of) light absorbed (by plant
pigments) at different wavelengths. 1
action spectrum: the quantity/rate of photosynthesis at each
wavelength. 1
[6]
2. (a) (i) amylase 1
(ii) amylose/starch is broken down to maltose. 1
(not: maltose and glucose)
(b) (i) there is no amylase/starch digesting enzyme in stomach tissue. 1
(not: ref. to acid/pH; allow consequential error from (a) (i)
(ii) duodenum tissue does not secrete amylase, pancreas does. 1
(c) 5cm3 starch suspension + 2cm3 deionised/distilled water/boiled tissue 1
[5]
Question Answer/Explanatory Notes Marks
Available
3. Natural active immunity
When an individual produces antibody;
and memory cells;
as a result of natural infection.
Artificial active immunity
When an individual produces antibody;
and memory cells;
as a result of vaccination/immunisation or description
Natural passive immunity
When an individual receives antibody produced by another individual/mother;
There are no memory cells;
It is short-lived immunity;
(Maternal antibodies transferred to the foetus) over the
placenta/to the offspring in breast milk/colostrum.
Artificial passive immunity
When an individual is injected with pre-synthesised antibody;
There are no memory cells;
It is short-lived immunity;
Tetanus antitoxin/rabies/rubella antibodies/ any suitable disease
[8]
4. (a) A Gram positive
bacillus/rod
B Gram negative
Coccus 4
(b) Gram +ve have a thicker cell wall (not: larger)
made of murein/peptidoglycan (not: lipopolysaccharide)
which retains the crystal violet/purple stain
or converse 3
(c) Red stained/Gram negative bacteria have extra layers in the/
more complex cell wall
which protect/give resistance to lysozyme/penicillin/antibiotics 2
(not: prevents osmotic lysis)
[9]
Question Answer/Explanatory Notes Marks
Available
5. (a) Salmonella/bacteria 1
(b) Indicate organisms with the same/similar antigens on the surface
Sub-groups or strains of a microbial species/bacteria (which may be
used to trace infections)
Identified by antibodies from serum 1
(c) Poisonous substances/toxins produced by the bacteria 1
(d) May already be dehydrated/immune systems may be unable to combat
infection/weakened immune system 1
(e) Bacteria are at a higher temperature if food is not refrigerated and so
multiply (eq) more rapidly/undercooked meat from barbecue 1
(f) Thorough cooking of meat/poultry/eggs (not: food)
storage in cold conditions/fridge
separate cooked and raw meat
prevent contamination (of food) by carriers/washing hands before
handling food 1
(Any 1)
[6]
6. (a) infection/pathogen will not be destroyed by the antibiotic if it is