WELSH JOINT EDUCATION COMMITTEE
CYD-BWYLLGOR ADDYSG CYMRU
General Certificate of Education Tystysgrif Addysg Gyffredinol
Advanced Subsidiary/Advanced Uwch Gyfrannol/Uwch
MARKING SCHEMES
JANUARY 2003
BIOLOGY
Page
BI1 1
BI2 8
BI4 14
18
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.
18
MARK SCHEME
BI1 - January 2003
1. / Monosac-charide / Disac-charide / Structural Polysac-
charide / Storage Polysac-
charide
Glucose is
an example of / / / (1)
Cellulose is
an example of / / / (1)
Amylose is
an example of / / / (1)
Maltose is an
example of / / / (1)
Insoluble / / / / / (1)
Deoxyribose is
an example of / / / (1)
Glycogen is
an example of / / / (1)
Total 7 marks
2. Double outer membrane (if drawing shows double membrane and label says outer membrane accept) / (chloroplast) envelope / inner and outer membranes;
(not: membrane)
Stroma;
Ribosomes;
Circular / ring / loop DNA (accept DNA without reference to circular in label if it is clearly circular in the drawing) / circular chromosome.
Thylakoids; (1 sac, not bracket to stack)
Grana / Granum (to stack);
Lamellae; (anywhere apart from stack)
Oil Droplets / oil / lipid; (not: fat / lipid molecule)
Starch (Grains); (not: starch molecule or drawn with double membrane)
Any five
If drawing very poor max 4 marks. (5)
Total 5 marks
3. (a) 3 (1)
/ (1)
-1 for each extra tick.
(ii) Any drawing with the 3 different chromosomes i.e. 3 shapes (with a different combination of filled not filled to those given in question e.g. all three filled or all three empty, largest one filled other two empty etc.) (1)
(iii) Half number of chromosomes/haploid;
Variation / genetically different;
Crossing over / chiasmata;
Diploid / original number of chromosomes is maintained when gametes fertilise OWTTE.
Independent assortment.
Any two (2)
(c) (i) Complete the table below to show the main difference between meiosis and mitosis.
1. Double / bivalents / homologous / synapsis / 1. Single chromosome
(allow: no bivalent)
2. Crossing over / chiasmata / 2. No crossing over
3. 2 chromosomes per spindle fibre / 3. 1 chromosome per spindle fibre
4. Whole chromosomes either side of equator / 4. 1 Chromatid either side of equator
5. Random assortment / 5. No random assortment
6. No division of centromere / 6. Centromere divided
7. At telophase DNA / chromosome number is halved / 7. Number stays the same / is not halved.
(not: daughter cells)
Any three points must match (3)
(ii) Interphase (1)
(allow: S phase)
Total 10 marks
4. (a) Zero / 0 (1)
(b) (i) 400Kpa (1)
(ii) 900Kpa (1)
(c) (i) Cell G (1)
(ii) Cell E (1)
(d) Plasmolysis [Plasmolysed] (1)
(not: incipient plasmolysis / flaccid)
(e) It would burst (swell) / lyse / water would move in. (1)
(not: turgid unless mentions lysis / gains weight)
Total 7 marks
5. (a) A Pentose sugar / deoxyribose (allow: 5 carbon sugar) (1)
B Phosphate (1)
(b) Hydrogen (Bonding) (not: H) (1)
(c) (i) Purine (1)
(ii) C Adenine (1)
D Thymine [allow a consequential error here] (1)
Reject abbreviations A/T / consequential error if C is uracil.
(d) Ring should cover any 1 base with 1 sugar and 1 phosphate (through dotted lines i.e. bond). (1)
(e) If 28% G then C must be 28% (1)
(28+28 = 56) / 100 56 = 44/(A+T = 44) (1)
T = 22(%) (1)
1 mark for each correct line.
Total 10 marks
6. (a) Linear scales (both) + good use of paper. (over 50% both directions) (1)
pH along X axis % up Y axis. Correct positions + axes labels on graph including % or proportion. (1)
Correct plots (-1 for each incorrect plot). (2)
Smooth lines drawn for curves. (1)
(b) (i) O / no activity (1)
(ii) Peak at 2 (± ½ pH) (1)
Narrow range (0 ® 5) (1)
(c) Alter (the shape) of the active site / destroyed / damaged;
(Extreme) changes will denature enzyme (allow: changes 3D shape if very clear);
Changes in pH alter the ionic / electrostatic charges (of the acid and base groups);
Inactive / lower activity with a small change.
Any three (3)
(d) Temperature (not: heat / room temperature);
Enzyme concentration (not: amount / volume);
Substrate concentrations (not: amount / volume / concentration solute);
Time.
Any two (2)
(e) Buffers (1)
Total 14 marks
7. (a) (i) Human genome project (not: description) (1)
(ii)
"Encouraging the transmission of 'desirable' traits and discouraging the transmission of 'undesirable' ones";
The use of genetic engineering for improvement of the human genome / designer babies, i.e. choosing genes;
Selective/controlled breeding of humans;
The sterilisation of those considered of low character or feeble-minded / abort fetuses with disease.
Any two (2)
(b) (i) Gene therapy is:-
Insertion of a new DNA / gene sequence. To counteract / correct a faulty gene (not: replace faulty gene unqualified). (1)
(ii) Introduce new DNA / normal genes into cells / body. (1)
(iii) Escape of DNA / possible introduction of other genes as well / activate oncogenes / cancer genes / not permanent/needs retreatment (not: causes cancer / ref. to cost / false hopes / takes time). (1)
Total 6 marks
8. (a) A Function of RNA polymerase (ref. to).
B The sequence of the bases on the DNA is the genetic code/
This determines the primary structure of a protein/sequence of a. acids.
C Transcription.
D Part of the DNA double helix unwinds / unzips / opens up.
E One of the DNA strands is used as a template for the formation of mRNA / mRNA is formed on the DNA.
F Free (RNA) nucleotides join to form mRNA.
G Bases bond C-G; G-C; A-U; T-A (not: complementary base pairing).
H Messenger RNA (transmits genetic information) from (the DNA in) the nucleus to ribosomes (in the cytoplasm).
I Ribosomes contain rRNA (and protein).
J Ribosomes are the site of protein / polypeptide synthesis / translation.
K There is a specific tRNA for every amino acid / or converse.
L Binding site of amino acid (on the tRNA). Accept diagram.
M The amino acid carried is determined by the anticodon on the tRNA.
N The mRNA has a series of codons.
O The anticodon on the tRNA will match up with the complementary codes on the mRNA or shown as letters on diagram.
P The codon is a triplet of bases (either codon or anticodon).
Any eleven (11)
Total 11 marks
(b) A There are protein (lined) pores in the membrane. Accept diagram of membrane.
B Diffusion is the movement of molecules from a region of high concentration to a region of lower concentration / down concentration gradient.
C The rate of diffusion will depend on
D The concentration gradient / distance / temperature / size of molecules. Any 2/4.
E (Diffusion) can only happen for lipid soluble molecules / O2 / CO2 / small uncharged molecules. (Any one) or converse.
F Water moves by a process of osmosis.
G (Water moves) from a region of high water potential / concentration to a region of lower water potential / down a concentration gradient.
H Facilitated diffusion (allows substances, which are not lipid soluble to cross being) helped by special carriers / pores.
I Facilitated diffusion, osmosis and diffusion do not require ATP / are passive. Any 2/3.
J Large molecules can enter by phagocytosis / endocytosis.
K Particles become enclosed by membrane to form a vesicle and are transported into the cytoplasm (accept diagram).
L Pinocytosis is entry of liquids (by the same mechanism as phagocytosis).
M Active transport requires energy / ATP.
N (Active transport) moves substances against a concentration gradient.
O Protein / Carrier molecules are used (in active transport).
P Ref. to membrane structure e.g. Phospholipid in membrane / fluid mosaic.
Any eleven (11)
Total 11 marks
MARK SCHEME
BI2 - January 2003
1. D = Stomata / stoma;
Exchange of gases (allow: CO2 in; not: allow water to escape) (2)
B = Palisade (mesophyll) layer;
(Main) site of photosynthesis/synthesis of sugars (2)
C = Air spaces; (not: spaces)
(Rapid) diffusion of gases (not: exchange of gases) (2)
A = (Waxy) cuticle;
Reduces water loss (not: protection)
(allow: prevents water loss) (2)
2 marks for each one for name, one for qual.
Total 8 marks
2. (a) A Tricuspid valve / atrio ventricular valve (1)
B Vena cava (1)
C (Dorsal) Aorta/aortic arch (1)
D Left Ventricle (1)
(b) 1 mark for position (between papillary muscle and line at edge of
heart.) (1)
1 mark for closed (If 1 only drawn, only this mark available) (1)
(c) Prevents valve inverting (not: support) (1)
(d) (i) Pacemaker in wall of right atrium/contraction initiated
in right atrium. (1)
(ii) To transmit wave of depolarisation to (apex of) ventricles
owtte. (1)
(iii) Wave of contraction starts at base of ventricles and moves
upwards (not: muscle stronger) (1)
(e) (i) Reduce dilation during systole;
Cope with high pressure.
Restrict diameter therefore increase blood pressure;
Vaso constriction/vaso dilation
Elastic recoil increases blood pressure/keeps blood flowing.
Any two (2)
(ii) So that it does not interfere with flow of blood/reduce
friction/blood flows more easily (1)
Total 13 marks
3. (a) A Light/solar energy/(sun)light (not: sun, allow: photosynthesis) (1)
B (Energy loss) Respiration (1)
C (Energy loss) Excretion/Egestion/production of faeces/urine/
waste (not: faeces/urine/wastage) (1)
(b) Third (1)
(c) (i) Spider (1)
(ii) Higher/maintaining body temp / Higher metabolic rate
(not: ref. to size) (1)
(iii) Less cellulose/fibre in diet/undigestible matter. (1)
(d) (i) (Could be) greater productivity in oceans / higher energy conversion
less support required in oceans, less cellulose etc./less egestion/
oceans mainly ectothermic animals, respiratory loss greater/
less muscular activity, support etc. in oceans, respiratory
rate lower.
Any one (1)
(ii) Any one of above but different. (1)
(iii) Less cellulose/lignin/undigestible material in grasses; (or converse)
Productivity could be lower in forest? (1)
(iv) Energy lost at each transfer, not enough energy in last trophic
level to support another layer. (allow: energy runs out) (1)
Total 11 marks
4. (a) (i) 95% saturation (1)
(ii) 44/45% saturation in muscle (1)
(iii) 571/560 ´ 106 (1)
(b) (i) To left of normal (1)
(ii) Does not become saturated at the pp of oxygen in environment/
At low pp oxygen does not release as much oxygen
(allow: does not have a strong enough affinity) (1)
(iii) In tissues with high pp. O2 no release of O2;
Small drop in pp O2 at lower pp O2 too much released/all or
nothing;
Less oxygen released at lower pp of oxygen (max 1) (1)
(c) (i) To right of normal;
Bohr effect. (2)
(ii) (High CO2 levels) (high respiration) causes more oxygen release;
at the same pp. of oxygen. (2)
(d) Higher affinity for oxygen;
Allow fetus to absorb oxygen from mother. (2)
Total 12 marks
5. (a) Surface area not increasing at same rate as volume, volume of cytoplasm
related to rate of use of oxygen and nutrients, surface area related to rate
of uptake by diffusion/SA: vol ratio not enough
maximum rate of diffusion of materials through cytoplasm/distance;
Accept reference to nucleus.
not able to exchange enough as it gets bigger.
(Allow: support qualified)
Any two (2)
(b) Large surface area;
moist skin/surface
blood supply close to surface;
rich/well developed capillary network in skin/good blood supply at
surface/skin
haemoglobin.
Any three (3)
(c) (i) Blood and water;
Flow in opposite directions. (2)
(ii) More efficient exchange of gases/constant diffusion/exchange across
whole lamella.
Concentration gradient maintained. (2)
Total 9 marks
6. (a) (i) Keep surface of cells moist/lubricated;
Medium through which materials can diffuse;
Supply nutrients / named nutrients to cells; e.g. O2
Take away waste products / named; e.g. CO2
Take away products of cells / named;
Ref. protection/support.
Any two (2)
(ii) Return excess (tissue) fluid;
to blood system/subclavian vein
Ref. lymphocytes/defence against disease (not: wbc unqualified)
Ref. absorption of fats/lacteals
Any two (2)
(b) Proteins (albumin) main osmotic material in blood;
Less protein easier for fluid to be lost from capillaries (balance between
osmotic and hydrostatic pressure changed);
Less water in tissue fluid reabsorbed;
Oedema is swelling caused by accumulation of tissue fluid.
Any three (3)
7. (a) Forestry/Fishing
A Habitat destruction / comment on destruction balanced ecosystems
B Reduction in biodiversity/owtte
C Qual of above e.g. loss of potentially important therapeutic plants /
reduction gene pool
D Soil erosion / dust bowls
E Increase in sedimentation/deposits
F Climate change/example/ref. to global warming
G Fall in CO2 reduction/raising CO2 levels/O2
H Reduction of population to below sustainable levels/numbers cannot be maintained - will be further decline
I Curtailment of breeding due to fewer mature fish
J Replanting