Bio Unit 2 All Topics Answers

1.2. (a) A Crista / cristae

B (Outer) membrane/inter-membrane space / eq envelope;

C Matrix ; 3

(b) Aerobic respiration / description /eq link reaction / Krebs cycleoxidative phosphorylation / electron transport chain;

Production of ATP; 2[5]

3. (a) A - chromatid;

B- centromere; 2

(b) Anaphase;

Chromatids separate / centromere splits

Move / pulled to (opposite) poles / ends of cell / ends of spindle to centrioles ;

By spindle fibres / microtubules 3

(c) Daughter cells genetically identical (to parent cell) /maintainschromosome number/eq; 1

(d) Interphase / G1 / S / G2 / cytokinesis / cleavage

If interphase or named stage - growth/synthesis of organelles

synthesis / replication of DNA / division of organelles

OR

If cytokinesis - division of the cytoplasm / formation of cell plate in plants ;

Points linked. [if give ‘telophase’and then describe division ofcytoplasm allow second mark] 2

[8]

1

4.

Name of organelle Description Function

Stack / group / eq, of,(flattened / curved), cisternae /tubules / sacs ;

Transport of lipids / storageof lipids / modification oflipids /formation of glycoproteins /modification of proteins /formation of secretory / eqvesicles / formation oflysosomes / transport ofcarbohydrates ;

Centrioles / centrosome;

Mitochondria ; Aerobic respiration / ATPproduction / ETC / oxidativephosphorylation / Krebscycle;

[5]

5. (a) anaphase ;

prophase ;

telophase ;

metaphase ;

[if ‘I’ or ‘II’, penalise ONCE] 4

(b) (i) (G lasts) 7.0 hrs (and cell cycle time is 14 hrs) / 18-11 ;

7 × 100 ÷ 14 ;

= 50 % ; 3

(ii) B ;DNA replication / DNA mass beginning to, increase / double ; 2

[9]

2

6. Note: Do not credit 'reduce water loss' alone, as this is stated in the question.

Thick cuticle ;

Impermeable to water or Reduces, transpiration / diffusion of water (vapour) / reduces evaporation ;

Few stomata / stomata on inside of leaf ;Reduces, transpiration / diffusion of water (vapour) / reduces evaporation ;

Leaf rolled / eq ;Reduces (exposed) surface area / stomata open into enclosed space / maintains high humidity inside leaf / reduces transpiration / reduces evaporation ;

Stomata in pits / sunken stomata ;Reduce air movement / increase humidity / reduces transpiration / reduces evaporation ;

Presence of hairs / eq ;Reduce air movement / trap moist air (next to leaf) / reduce diffusion (gradient) / reduces transpiration /reduces evaporation ;

Presence of hinge cells ;To curl leaf ; 2 + 2 + 2

[6]

7. (a) Tubifex / sludgeworm / rat-tailed larva / midge larva / Chironomus larva / bloodworm / gnat larva / mosquito larva; 1

3

(b) Haemoglobin / respiratory pigment (in blood) ;Picks up oxygen (at low external oxygen concentrations) / very high affinity for oxygen ;

Very thin body wall ;Short oxygen (diffusion) pathway ;

Blood (vessels) near body surface ; Short oxygen (diffusion) pathway ;

Waving tail ; Circulates water next to body / eq. ;

Reference to breathing tube / eq ;Goes to surface / to obtain oxygen from the air ; 2 + 2

max 4

Presence of hairs / wing cases / elytra ;To trap an air bubble ;

[Credit other correct example][5]

8.

Feature Prokaryotic Cell Eukaryotic cell

Cell surface membrane

Plasmids X

Ribosomes

Mitochondria X

[4]

Any two correct boxes for one markBlanks are incorrectCircle correct answersPut in appropriate number of ticks for total mark

9. (a) centrioles / centrosomes ;asters ;no cell wall ;[ignore chloroplasts and vacuole] 2

4

(b) A chromatid / chromosome / daughter chromosome ;B spindle (fibres) / microtubules ; 2

(c) anaphase ; [ignore I or II] 1

(d) 80 ÷ 1000 ; [accept 80 to 83 or 8 to 8.3]0.08 mm / 0.008 cm / 80 m ; [accept answer consistent with measurement] 2

[7]

10. (a) prevent, entry / exit, of water ;by osmosis ;which may affect / eq, organelles ; 2

(b)

Pellet Organelle

A nuclei ;

B mitochondria ;

C ribosomes ;

2

(c) glucose / monosaccharides / disaccharides / sugar ;glycogen ;proteins / (poly)peptides ;enzymes / suitable named example ;ions / named example ;amino acids / named example ;lipids / phospholipids / triglycerides / fats ;microtubules / centrioles ;microfilaments ;RNA / mRNA / tRNA ;[accept other correct substances present in liver cells] 2

(d) two membranes shown [M] ;inner membrane shown folded [F] ;membrane / envelope ;intermembranal space ;cristae ;matrix ;ribosomes / DNA, in matrix ;stalked particles / ATPase ; 4

5

(e) to produce (large amounts) of ATP ;by, aerobic respiration / Krebs cycle / electron transport chain ;(because) liver cells are (metabolically) very active / eq ; 2

[12]

11. (a) A flagellum ;B DNA / (bacterial) chromosome ;C cell wall ; 3

(b)

Markingpoint

Prokaryotic cell Eukaryotic cell

1 Smaller Larger ;

2 Do not have a nucleus / nucleolus / have a nucleoid

Have a nucleus / nuclear envelope / nucleolus (allow description) / no nucleoid ;

3 Do not have membrane-bound organelles / absence of named organelle

Have membrane-bound organelles / presence of named membrane-bound organelle ;

-

4 Smaller / 70S ribosomes Larger / 80S ribosomes ;

5 Mesosomes / description of infoldings

No mesosomes ;

6 Circular DNA Linear DNA ;

-

7 No histones / chromosomes Histones / chromosomes ;

8 Murein / mucopeptide / peptidoglycan cell walls / no cellulose

Cellulose cell walls (if present) ;

9 Flagellum with no microtubules / eq / reference to basal structure

Flagellum with microtubules / 9+2 arrangement / reference to basal structure ;

3[6]

6

12. (a) Reference to named stain (acetic orcein / acetocarmine / Feulgens / Schiffs) ;Warm / heat ;Break open tip with (mounted) needle /eq ;Mount in stain / acid / water ;(gently) squash under coverslip / eq ; max 4

(b) (i) A ; 1

(ii) C ; 1

(c) Synthesis / division / multiplication of organelles (or named organelle) ;Growth ;Replication of DNA/ chromosomes ;Protein synthesis / name of specific protein being synthesised ;Any normal cell activities, named example (e.g. respiration) ; max 2

[8]

13. (a) A Pollen tube ;B Tube nucleus ; 2

(b) One, fuses / fertilises / combines, with female nucleus / egg cell / eq ;To form zygote ;Which is diploid ;One fuses with polar nuclei / fusion nucleus / primary endosperm nucleus ;To form endosperm (nucleus) ;Which is triploid / 3n ; 4

(c) (i) 15% ; 1

(ii) (Germination rate of) both decreases ;(Germination rate of) Bauhinia always greater than that of Camellia // converse ; [greater at all concentrations must be implied](Germination rate of) Camellia reaches zero at 25%, Bauhinia minimum at30% / does not reach zero / eq ;Above 30 % / this (germination rate of) Bauhinia (starts to) increase(Camellia stays at zero) ; 3

[10]

7

14. Presence of respiratory pigment / haemoglobin ;To take up oxygen (at low partial pressures) / high affinity for oxygen ;Presence of breathing tube / siphon / eq ;To reach the air / to reach above surface ;Waving tail / eq ;Circulates water near body / maintains oxygen, diffusion / concentration, gradient ;Gills ;Increase surface area ;Hairs ;Trap bubble of air ;Flattened / elongated body ;Increase surface area ;Capillaries close to surface / thin body wall ;Short diffusion distance ; 2 + 2

[4]

15. (a) B Spermatagonium ;C Spermatid / spermatocyte ; 2

(b) (i) C / D ; 1

(ii) Meiosis I / reduction division ;Homologous chromosomes ;Attachment to spindle fibres ;Separate in, metaphase (I) / anaphase (I) ;To two opposite, poles / ends of cells ; 4

(c) Flagellum / tail – locomotion / eq ;Acrosome – (hydrolytic) enzymes to penetrate egg membrane / eq ;Large / many, mitochondria to provide, energy / ATP ; 2

[9]

16. (a) (i) (single) membrane ;Contains {hydrolytic / digestive / zymogen} enzymes ;[accept suitable named enzyme]

Reference to size (accept up to 1 m) ; 2

(ii) Isolation of enzymes ;Break down / eq of {ingested material / bacteria} ;Autolysis / self-digestion ;Breakdown of (old) organelles ; 2

8

(b) 0 – 10 hours Increase in radioactivity ;10 – 12 hours Amount of radioactivity remains constant ;After 12 hours Fall in amount of radioactivity ;OR0 – 8 hours Increase in radioactivity ;8 – 14 hours Amount of radioactivity remains relatively constant ;After 14 hours Fall in amount of radioactivity ;

No radioactivity present in white blood cells at the beginning and someremaining inside white blood cells at the end ; 3

(c) (hydrolytic enzymes) digesting the bacteria ; 1

(d) Degraded bacteria are expelled from cell / eq ;By exocytosis ;Digested molecules are (still) radioactively-labelled ; 2

(e) Not all bacteria engulfed / some {radioactivity / labelled amino acids}still present in supernatant / eq ; 1

[11]

17. Points accepted in correct context only

1. Occurs in ovaries and testes ;2. Formation of spindle / reference to centrioles ;3. (Prophase) condensation of chromosomes / disintegration of nuclear

{membranes / envelope} / disappearance of nucleolus ;4. (Meiosis I) homologous chromosomes pair / bivalents form ;5. And attach to spindle at {metaphase plate / equator} ;6. Each chromosome consists of two chromatids ;7. Crossing over / chiasma ;8. (Anaphase I) separation of chromosomes ;9. To opposite poles of cell ;10. Pulled by spindle fibres / microtubules ;11. (Meiosis II) sister chromatids separate ;12. {Haploid / n} {cells / gametes} formed ;13. Fertilisation restores {diploid / 2n} number ;14. Reference to genetic variation ;15. Reference to the production of four sperm, and one {ovum / egg} plus

{two / three} polar bodies ;[10]

18. (a) (i) Spermatagonium / primordial germ cell ; 1

(ii) M clearly shown between secondary spermatocyte and spermatid ; 1

9

(b) A Mitochondrion ;B Flagellum / microtubules / axial filaments ;C Acrosome / lysosome ; 2

[All correct for two marks, two correct for one mark]

(c) 1. Seminal fluid ;2. From secretions of {prostate gland / Cowper’s gland / seminal vesicles} ;3. Secretions contain {nutrients / mucus / enzymes / lubricant} ;4. Seminal fluid + sperm = semen ;5. {Stored / collected} in {vas deferens / ejaculatory bulb of urethra} ;6. Erection of penis ;7. By increased blood {volume / pressure} ;8. Inserted into vagina ;9. Muscle contractions cause ejaculation (of sperm) ; 5

[9]

19. (a) Seminiferous {tubule / tube} ; 1

(b) Cell A Primary spermatocyte ;

Cell B Spermatid ; 2

(c) 1. Reducing chromosome number / haploid from diploid / 2n to n / correctreduction ;

2. So diploid reformed at fertilisation / eq ;

3. Genetic variation ;

4. Four {sperm / gametes} produced ; 3[6]

20. (a) 1. Low oxygen (concentration) ;

2. Reference to (breathing) tube / eq ;

3. To obtain oxygen / to exchange oxygen and carbon dioxide ;

4. From above surface of water / from air ;

5. Reference to hairs or lipids to prevent waterlogging of tube ;

6. Reference to {respiratory pigment / haemoglobin} ;

7. With a high affinity for oxygen ; 4

10

(b) Reference to {claws / hooks} (on legs) ;

To hold onto stones / eq ;

Streamlined / flattened shape / aerodynamic / hydrodynamic ;

Less resistance to flowing water / hides under stones ; 2[6]

21. Tissues are groups of (similar) cells performing similar functions;

Organs are a number of tissues that perform a function 2[2]

22. (a) (i) BDAC; 1

(ii) Metaphase; [ignore I and II] 1

(b) (i) DNA replicates;Cell division / cytokinesis; 2

(ii) Mitosis / G2 and mitosis; 1

(iii) {l5/20} hours; 1[6]

23. (a) A Nucleus/chromatin/nucleoplasm;B Mitochondrion; 2

(b) Correctly measured length;(Length) ÷ 5000;Correct answer in m; 3

(c) 1. (molecules/proteins) pass into the{cisternae/eq}of the RER;

2. Vesicles {break off (from cisternae) / form};

3. (molecules) carried to Golgi / (vesicles) fuse with Golgi;

4. (proteins) concentrated;

5. Modified / carbohydrate added / become glycoproteins;

6. Vesicles {break away (from Golgi) / move to cell membrane};

7. (vesicles) fuse (with cell membrane);

8. Reference to exocytosis; 5[10]

24. (a) Anaphase;II; 2

11

(b) (i) 23; 1

(ii) 46; 1

(iii) 46; 1

(c) 1. In seminiferous tubules (of testis);

2. At puberty / continuous through adult life / 12-16 years to 65-70 years;

3. Reference to {germinal cells / eq} divide by mitosis (to formspermatogonia);

4. Spermatogonia divide by mitosis;

5. Form {primary spermatocytes /type B};

6. Divide by meiosis I;

7. Form secondary spermatocytes;

8. Divide by meiosis II;

9. Form spermatids;

10. Any reference to {correct male hormone / Sertoli cells} referenceto differentiation of spermatids to sperm; 5

[10]

25. (a) (Extensive root system) increases surface area;

For uptake of water;

Near surface so can take up water rapidly when it rains / eq; 2

(b) Storage;Of water;Allows easy movement of water through walls / allows expansion of cells; 2

(c) Reduced surface area;Fewer stomata;Reduces {transpiration / water loss} / converse;Protection against herbivores / eq;Spines trap humid air; 3

[7]

12

26. (a) Reversible damage is {not permanent / eq} and irreversible damage is{permanent / eq};

Pipeline laying causes damage but {land / soil / eq} replaced;Building treatment works is permanent because {land cannot be replaced/ habitat is destroyed}; 2

(b)

Area Type of development

Area

/ m2

Ecological category

Units ofdamage

Reversibledamage

Irreversibledamage

p 42 000 42 000

q 2 500 2 500

r 3 000 3 000

s 2 500 2 500

t 10 000

Totals 60 000 18 000 42 000

1. Units of damage calculated for p, q, r, s and t;

2. Damage for area p assigned to irreversible damage and damage forareas q, r, s and t assigned to reversible damage;

3. Totals correct; 3

(c) 1. (Total ecological) damage at Site 1 greater than at Site 2;

2. Reversible damage at Site 2 less than at Site 1 / irreversible damage at Site 2 greater than at Site 1;

3. Two category 5s at site 2 AND one category 5 at site 1;

4. Manipulation of figures to compare magnitude of damage; 3

(d) Number of {species / different types of organism / different kinds of organism}; 1

(e) 1. Distance from shore / different lengths of pipeline;

2. Tidal movement / tides;

3. {Strength / direction) of currents;

4. Reference to wash back / eq;

5. {Strength / direction} of winds;

6 Wave action;

7 Depth of pipeline / depth of water;

8. Temperature of water / oxygen concentration in water; 3

13

(f) 1. Addition of {minerals / nitrates / phosphates / nutrients} / reference to eutrophication;

2. And organic solids;

3. (Leads to) increased growth of {algae / seaweeds / plants / producers};

4. More food for {herbivores / primary consumers};

5. (So) {herbivores / primary consumers} increase in number;

6. More food for carnivorous fish; 4[16]

27. (a) (i) Endoplasmic reticulum / mitochondrion / mitochondria /membrane-bound organelles / internal membranes; max 1

(ii) Bacterium / named bacterium / bacteria / blue-greenalgae / cyanobacteria; 1

(b) (i) Ribosome;

(ii) Protein synthesis;

OR

(i) (Rough) endoplasmic reticulum / intermembranal space;

(ii) {Transporting / trafficking / folding / synthesising} proteins; 2

(c) B (Outer mitochondrial) membrane / doublemembrane / intramembranal space / double envelope;

C Crista / infolding of (inner mitochondrial) membrane / innermitochondrial membrane; 2

[6]

28. (a) 1. Tail / flagellum;

{To swim / to propel it} to the {egg / ovum / vitelline membrane};

2. Small(er) size;

Makes it easier for it to swim / to aid mobility / makes it possibleto produce them in large numbers;

3. Haploid number of chromosomes / only one of each chromosome/ (only) 23 chromosomes rather than 46;

So {normal / diploid} number restored at fertilisation;

4. Acrosome / sac of enzymes; To digest way (in)to egg;

5. Mitochondria; Energy for swimming / eq; 4

14

(b) (Mitosis and) meiosis; 1

(c) (Produces) {biological / genetic} variation;No two sperms the same;

Many sperms do not reach egg / increases chances offertilising eggs;Selection for {fittest / eq} sperm;Some sperms defective; 2

[7]

29. (a) Vacuole;

Tonoplast;

Plasmodesmata / plasmodesma;

Pits;

Chloroplasts / plastids;

Starch grains / amyloplast;

Calcium pectate qualified / middle lamella; 3

(b) (i) P Sclerenchyma / (wood) fibres;

Q (xylem) vessel {cell / element}; 2

(ii) 1. Cellulose microfibrils held together by hemicelluloses;

2. Reference to orientation of microfibrils to givemaximum support in stated direction;

3. Reference to H-bonds;

4. Lignification makes walls {stiffer / rigid / thicker};

5. Cellulose walls are thicker / secondary cellulose; 3

(c) (i) Paper production / (production of) {cloth / fishing nets / fabric} /biocomposites / ropes / string / animal feed / biofuel / fermentedto make biogas / green manure; 1

15

(ii) Nettles will regrow after stems have been harvested / harvestseeds and sow for new crop / no need to buy seeds / idea thatone can always grow more;(as opposed to) use of non-renewable resource / namednon-renewable resource e.g. oil / if used as (bio)fuel{carbon dioxide output is equal to carbon dioxideinput / carbon neutral};Not causing deterioration of (good) agricultural land / eq; 2

[11]

30.

Name of organelle Two features of structure One function

Golgi (apparatus /body);

Cisternae / {flattened / membranous /network} {sacs / tubules};

Ribosomes;

{Transport / storage} ofproteins / synthesiseproteins / translation;

(Contains) {thylakoids / lamellae /grana};

(Contains) {stroma / chlorophyll / DNA/ starch granules};

(surrounded by) two membranes / double membrane / envelope;

[6]

31. (a) Root tip / shoot tip;Dividing cells / meristem; 2

(b) (i) To make the {chromosomes / chromatids / DNA} visible; 1

(ii) Acetic orcein / acetocarmine / Feulgens / Schiffs / any othercorrectly named stain; 1

(c) To {get a single layer of cells / spread out cells}; 1[5]

16

32.

Prokaryotic cell Eukaryotic cell

Ribosomes present

Cell diameter usually more than 20 µm

Cell may contain plasmids

DNA combined with protein into chromosomes

Nuclear membranes present

Cell wall always present

[5]

33. {Alpha / α} glucose;{Beta / β } glucose;More than two / several / many;Glycosidic;Insoluble;Energy / glucose;Hydrogen;

[7]

34. (a) 1. (Dead cells so) {no contents / hollow / (like)tubes / (like) pipes} / reference to lumen;

2. {No / reduced} {end / cross} walls;

3. Lignin qualified with reference to water e.g.waterproofing / strengthens to withstand pressure;

4. Pits for lateral movement (of water); 2

(b) (Forces of) adhesion; Intermolecular force between waterand {cellulose / lignin}; (Forces of) cohesion; Intermolecular force between water molecules; Pulled up xylem by transpiration / correct reference toevaporation as driving force; Difference in water potential / (hydrostatic) pressure; Root pressure / described in terms of osmosis in roots; 4

17

(c) (i) Intercellular cement / calcium pectate / middlelamella / helps to hold cells together;

(ii) For making chlorophyll / enzyme cofactors;

(iii) Making {protein / DNA / RNA / ATP}; 3[9]

35. (a) A Mitosis; B Meiosis; 2

(b) (i) Fertilisation / syngamy; 1

(ii) Zygote / diploid cell; 1

(c) X Y Z Acrosome; Nucleus;Mitochondria; 3

[7]

36. (a) Protection (of plant) from (bacterial) disease; 1

(b) (i) Correct reference to {bacteria / bacterial} innoculum;{Sterile / aseptic} techniques; Incubation / left to growfor a time; At temperature in the range 25 – 40 ˚C / for24 hours (accept up to 5 days); Correct reference to using aPetri dish or similar suitable piece of apparatus / correctreference to use of {a medium / agar};(If antibacterial substance is present) {clear / bacteria-free}zone around disc; 4

(ii) A bigger {clear / bacteria-free} zone than with garlic meansthe new substance is a more effective antibacterial agent / converse;Keep in same conditions / use same dish;Specific reference to any two variables to be standardisede.g. {mass of plant material used / incubation time / incubationtemperature / volume of extract used / size of filter paperdisc / type of filter paper / etc.};;Specific reference to quantitative means of comparing thedifferences in size of the clear zones; 3

18

(c) {Food preservative / food additive} to counteract{disease / food poisoning} / (chemotherapeutic) medicine tofight bacterial infection / {disinfectant / antiseptic / antibiotic} / toothpaste; 1

[9]

37. (a) Conflict with {farmers / agriculture } / eq / destruction of naturalhabitat; Isolated populations breed less successfully; Reference toclimate change in habitat; Removal of prey species / reference tofood chain; {Poaching / eq} / example of why tigers are removede.g. chinese medicine; 2

(b) (Breed from animals that are) {unrelated / from the wild / from anotherzoo / from outside the programme};

{Maintaining / increasing} breeding population; Different genetic makeup (from existing tigers) / introductionof new genes / eq;

Prevents {inbreeding / homozygosity} / promotes heterozygosity / less risk of genetic disorder; {Genes / alleles/ eq} mixed / larger gene pool; Replace genes lost as captive animals die; [allow converse of points] 3

(c) Tigers occur in a wide variety of natural habitats;(90% is a) high proportion of the different alleles / keepsmany different alleles in the population;Provides variety in phenotype;Allows adaptation to {new / natural} environment;Some individuals will survive {changed / different}conditions / similar organisms would be affected in thesame way by adverse environmental change;

Maintain {gene flow / similarity} to wild population / preventloss of wild characteristics / successful breeding between wildand captive populations; 4

[9]

38. Nuclear {membrane / envelope} / nucleolus;

Centrioles;

Metaphase;

Centromeres / kinetochore / chromosome;

Anaphase;[5]

19

39. (a) (i) A Flagellum;

B DNA / bacterial chromosome; 2

(ii) Glycogen; 1

(iii) Made of {peptidoglycan / murein} / does not contain cellulose; 1

(b) Correct measurement: {80 / 81} mm;

Correct division: ÷ 6000;

Correct conversion to m;

[Maximum 2 marks if answer is incorrect, correct answer: 13.3 / 13.5] 3[7]

40. (a) (i) (Inner) membrane of mitochondrion {is folded / forms cristae};(Inner) membrane of mitochondrion has {ATPase / stalked particles /electron carriers};Nuclear membrane has pores;(Outer) nuclear membrane is continuous with the endoplasmic reticulum;(Outer) nuclear membrane has ribosomes; 2

(ii) Chloroplast; 1

(b) 1. Cylindrical;

2. Occur in pairs;

3. Lie at 90° to each other;

4. Made of microtubules;

5. Arranged in {triplets / nine groups};

[Maximum 2 marks from marking points 1-5]

6. Reference to spindle formation / organisation;

7. Reference to {microtubule organising centre / assembling the tubulin}; 3[6]

41. (a) (i) (Chromosomes) condense / become visible / eq;

Presence of homologous chromosome pairs / (form) bivalents / synapsis;

Attach to spindle (fibres) ; [accept once, either here OR in (a)(ii)]

Reference to crossing over / reference to {chiasmata / genetic materialexchanged); 2

20

(ii) (Chromosomes) arranged at {equator / middle of cell};

{Bivalents / homologous chromosomes / very clear description} startto separate;

Attach to spindle fibres; [accept once, either here OR in (a)(i)] 2

(iii) Centromeres divide / eq;

Each chromosome separates into two chromatids / the chromatids separate;

(Separated chromatids) move to opposite poles; 2

(b) (i) {Secondary / 2°} oocyte; 1

(ii) {Secondary / 2°} spermatocyte; 1[8]

42. (a) Function: Photosynthesis / {absorb / trap} light;

Reason: Near top of leaf;

Cells contain [chloroplasts / chlorophyll};

Reference to densely packed cells; 3

(b) Buoyancy / eq;Storage of [oxygen carbon dioxide gases)Allows (rapid) [diffusion / movement) of [gases named e.g.); 2

(c) To enable {diffusion / uptake / exchange} of {gases (from air) / carbon dioxide / oxygen};

If in lower epidermis would let in water; 2[7]

43. (a) Number / range / variety of species;

Range of taxa / eq;

{Variety / diversity} within species;

{Variety / diversity} of ecosystems; 2

(b) {Identify / classify / name} organisms / eq;

Recognise new species; 2

(c) Correct working (56 250 – 53 820) (= 2430) ÷ 56250 x 100;

Correct answer = 4.32 % / - 4.32 % ;

2 marks for correct answer with no working shown;; 2

(d) 1. Loss (of rainforest) is not that bad;

21

2. Main means of subsistence / e.g. {growing food / obtainingfuel / building materials} / eq;

3. Can’t afford reforestation;

4. Can’t afford fertilisers (to improve existing farmland);

5. Allows exploitation of resources for profit / benefit economy;

6. Too difficult to enforce regulations;

7. {Ancient / existing} land rights;

[Maximum 4 marks from marking points 1-7]

8. Benefit tourism in Honduras;

9. Rainforests help to {prevent / slow down} globalwarming / reference to CO2 levels;

10. Reference to other environmental benefit of keeping forests;

11. Prevent loss of {habitat / niches / shelter / eq} for wildlife;

12. Prevent loss of {species / biodiversity};

13. Provide means of sustainable exploitation (of forest);

14. Prevents loss of potential medicine;

15. Regulation would make government unpopular; 5

[Maximum 4 marks from marking points 8-15][11]

44. (a) Measure {growth / height / number of leaves / mass / dry mass};

Growth with copper and {without copper / control / range ofcopper concentrations};

Reference to controlling variables;

Reference to {repeats / means / calculation of percentage growth}; 2

(b) High tolerance plants grow on {site B / eq};

Tolerance genes from {mine site / site B};

Carried by {pollen / seeds};

To {downwind site / site C};

Tolerance higher downwind than upwind; 3

22

(c) Plants compete / eq;

For {ions / water / nutrients / nitrates / light / space / eq};

Tolerant plants less well adapted / converse / eq;

So tolerant plants {smaller / less dry mass} / converse / eq;

Idea: Results are due to competition only because trays 1and 3 growing the same;

Manipulated figures; 4

(d) Decreases / more non-tolerant;

No benefit;

Competes less well; 2[11]

45. (a) A Nucleus / nucleoplasm / chromatin / nuclear {envelope / membrane};

B Chloroplast / stroma;

C DNA / chromosome / nucleoid; 3

(b) Cell wall of leaf cell is made of cellulose / bacterial cell wall is not made ofcellulose / bacterial cell wall is {peptidoglycan / mucopolysaccharide} /plantcell wall is not made of peptidoglycan / mucopolysaccharide; 1

(c) To enable cell to move (through medium);

Rotates / eq;

Any valid reason for movement; 2[6]

46. (a) 1. Reference to named stain (acetic orcein / acetocarmine /Feulgens / Schiffs);

2. {Warm / heat} (with the stain / acid);

3. Break open tip (with needle / eq);

4. {Mount / eq} in {stain / acid / water / glycerol};

5. (Gently) squash under coverslip / eq;

6. Warm (gently to intensify stain); 4

23

(b) 1. Telophase is the longest stage;

2. Anaphase is the shortest stage;

3. Correct manipulation of figures to compare any two phases;

4. Any two actual times given e.g. {prophase 29.16 mins /metaphase 16.80 mins / anaphase 8.40 mins / telophase 33.36 mins}; 3

(c) (Use the equation to) work out actual time of each phase;

Total all four times;

OR

Add up all 4 percentages;

{Substitute into equation / eq} / Multiply by 100

1200

; 2[9]

47. (a) Stack of at least three cisternae;

Cisternae curved / showing {budding / fusing} vesicles / eq;

{Cisternae / sacs / vesicles} labelled; 3

(b) (i) Level of radioactivity falls;

Protein moving out (of the RER); 2

(b) (ii) 1. (In first 20 minutes) there were no secretory vesicles / onlynon-radioactive material in vesicles;

2. (Because) radioactive proteins have not yet reached the vesicles;

3. (Because) {proteins / radioactivity / eq} has yet to pass intoGolgi apparatus;

4. From RER (into Golgi);

5. (After 20 minutes) reference to formation of vesicles(from Golgi) now containing (radioactive) protein; 3

[8]

24

48. (a) Anther / pollen sac / microsporangium / pollen mother cell; 1

(b) Anaphase;

II; 2

(c) 7;

7;

14;

21; 4[7]

49. (a) (i) M written between secondary follicle and part Q; 1

(ii) Graafian follicle / mature follicle; 1

(iii) Oestrogen;

Progesterone; 2

(b) 1. Sperm in {Fallopian tube / eq};

2. Release of enzymes (from acrosome);

3. Idea that enzymes digest channel on layers around secondary oocyte / eq;[accept ovum]

4. Fusion of membranes;

5. Reference to second meiotic division (of secondary oocyte);

6. Reference to fusion of two nuclei;

7. Reference to change in permeability of egg membrane; 3[7]

50. No mark scheme available

25

51. Unit 2B

Introduction could include reference to the structure of xylem tissue in plants –

Roles of diffusion and active transport in the uptake of mineral ions –

Structure of the root –

Movement of water (plus dissolved mineral ions) through the plant –

Apoplast, symplast and vascular pathways –

Role of the endodermis –

Functioning of the transpiration stream –

Structure of vessels and their contribution to the movement of water –

Unit 5B

Functions of:

Nitrate ions –

Phosphate ions –

Magnesium ions –

[some candidates might refer to the transport of mineral ions to sinks in the phloem]Scientific content 11 marks

Balance 2 marksCoherence 2 marks

[maximum 15]

ESSAY MARK SCHEME

Total maximum mark available: 1511 available for Scientific content2 available for Balance2 available for Coherence

26

Scientific content (S)

Scientificcontent (S)

Description

11(good)

The essay demonstrates a sound understanding of the topic, contains a significant amount of material relevant to two (or more) Units (including A2 units) of the specification, and includes suitable examples where appropriate.The candidate has clearly and coherently linked together information from different parts of the specification.

9(above

average)

An above average essay, with accurate content. The essay includes a good balance of material from two (or more) Units (including the A2 units), and examples where appropriate.There may be some minor factual errors.

7(average)

The essay includes relevant information from two (or more) Units (including A2 units), and the candidate links together some facts and principles.Some examples are included.There may be some minor factual errors.

5(below

average)

The essay includes some generally factually accurate and relevant material, and there is some attempt to link material from more than one Unit. However, the discussion lacks details, particularly of A2 Units.

3(poor)

There are some correct facts, but the essay lacks depth and accuracy. Little or no relevant information from A2 Units is included.

1(poor)

There are very few correct facts. The essay is generally superficial and inaccurate.

0(poor)

No correct, or relevant, information included.

Note: If a scientific content mark of 0, 1, or 3 is awarded, it is very unlikely that a balance mark of more than 1 is appropriate.

S = 11 marks

27

Balance (B)

2 Most of the main topic areas outlined are coveredSome discussion of each of the areas chosen, illustrated with suitable examples where appropriateMaterial included is all relevant to the topic and the candidate has linked information from more than one area of the specification.Few, if any, errors

1 Some of the main topic areas outlined are covered.Some discussion of each of the areas chosen.Some irrelevant material included.There are some examples which link together different areas of the specification.Some errors

0 Very limited account, possibly only one aspect chosenMaterial mostly irrelevantNo examples of the candidate linking information from different topicsLarge number of errors

B = 2 marks

Coherence (C)

2 Material logically presented, with little or no repetitionEssay has coherence, ideas are developed well; continuous prose used throughoutEssay has an introduction and a conclusion, summing up the main pointsTechnical terms have been used correctlySpelling, punctuation and grammar are sound

1 Material is presented in an orderly way and some ideas developedContinuous prose used throughoutThe introduction and conclusion may be present, but briefTechnical terms are used and generally in the correct contextSpelling, punctuation and grammar are generally sound

0 Essay style not usedMaterial in note form or numbered pointsVery poor standard of spelling, punctuation and grammar

C = 2 marks

28

52.

Typical plant cell Typical animal cell

Cellulose cell wall

Chloroplasts

Cell membrane

Large central vacuole

Chromosomes

Centrioles

Cytoplasm

Stored starch

[One mark for each correct row][7]

53. (a) C D B E A;; 2

[Two error = 1 mark, more than two errors = 0 marks]

[Allow one mark for D B E A C]

(b) (i) Root tip / (just behind) last 4-5 mm of root; 1

(ii) (Ethanoic / acetic / propionic) orcein / feulgen / toluidene blue /haemotoxalin; 1

(c) (i) (DNA) replication / S1; [do not credit reference to prophase / interphase] 1

(ii) {DNA / chromosomes} {doubled / copied} / new set of{chromosomes / DNA} forms / eq; 1

[Allow replication if not given in part (i)][6]

54. (a) 1. Glucose;

2. Hydrogen;

3. Microfibrils / fibre;

4. Strong(er) / thick(er) / stiff(er) / rigid;

[Do not credit hard]

5. Waterproof / impermeable; 5

[Allow marking point 4 and 5 either way round][5]

55. (a) A Metaphase ;

29

B Prophase ;

C Telophase ; 3

(b) 1. Chromatids separate / centromere splits ;

2. Moved to (opposite) {poles / ends / centrioles} ;

3. By spindle fibres / microtubules ;

4. Shortening / eq ; 2

(c) Daughter cells genetically identical to parent cell / maintainschromosome number / eq ; 1

[6]

56.

StatementFirst division of

meiosisSecond division of

meiosis

Pairing of homologous chromosomes occurs

Each chromosome consists of a pair of chromatids during prophase

Crossing over occurs and chiasmata are formed

Independent assortment of chromosomes occurs

[Any two correct responses = 1 mark]

[Blanks are incorrect]

[ is incorrect][4]

57. (a) 1. Reference to streamlined shape ;

2. Less resistance to water /eq ;

3. {Legs / feet } with {hooks / claws} ;

4. Gripping substrate / eq ;

5. Gills (on abdomen) ;

6. For gas exchange in water / eq ;

7. Antennae ;

8. Detecting water current ; 4

30

(b) (i) 1. Presence of haemoglobin / eq ;

2. For uptake of oxygen /with high affinity for oxygen ;

3. Presence of breathing tube / eq ;

4. To obtain oxygen from air /eq ;

5. Gills ;

6. To increase surface area (for uptake of oxygen) ;

7. Lower rate of respiration ;

8. Less oxygen required ; 4

(ii) 1. (Numbers increase as) pollution decreases ;

2. (and) oxygen levels increase ;

3. Less competition (from other species) / less predation ;

4. More food available ;

5. Larvae move down stream ; 2[10]

58. (a) 1. Prevent extinction;

2. By keeping breeding populations / where natural habitat lost;

3. Breed / breeding programme to increase numbers;

4. For reintroduction to wild / reference to genetic diversity / eq;

5. Study animals / research;

6. Better understand means of conservation;

7. Education;

8. Raise awareness / support for conservation; 4

(b) 1. Introduce new / unrelated animals / reference to sperm bank;

2. Introduce new alleles / genes / increase gene pool;

3. Prevent inbreeding;

4. Maintain genetic diversity;

5. Stud books / pedigree records;

6. Collaboration between zoos;

7. Reference to embryo technology; 2[6]

31

59. Diagram mark(cell wall, no nucleus, slime capsule, pili or membrane-boundorganelles, genetic material or flagellum) ;

Any 3 labelled structures:

Cell wall ;

Invaginations / mesosome ;

Flagellum ;

Bacterial chromosome / circular DNA ;

Plasmid ;

70s ribosomes[4]

60. (a) A Granum / (stack of) thylakoids ;

B Stroma ;

C Starch grain ; 3

(b) Correct width measured (mm / cm) ;

Width / 5000 ;

Correct conversion into µm ; 2

(c) Palisade (mesophyll cells) ;

Spongy (mesophyll cell) ;

Guard(cells) ;

[“Mesophyll” unqualified = 1 mark] 2[8]

61. (a) (i) 4 ;

(ii) 4 ; 2

(b) 1. Idea of using a short length of root tip ;2. Ref. to acidification ;3. Add {acetic orcein / acetocarmine / Feulgens stain /

Schiffs reagent / Toluidine Blue / Lactoproprionic Acid} ;4. Warm / heat ;5. Break open tip (with mounted needle / eq) ;6. Mount/ eq in {stain / acid / water} ;7. (Gently) squash under coverslip or slide ;8. Warm slide (to intensify staining) ; 5

32

(c) (i) Metaphase /prophase ; 1

(ii) Spindle is made during prophase ; 2

(if there is no spindle) {there is nothing for the chromosomes to attach to(in metaphase)} / {chromatids cannot be pulled apart(in anaphase)} ;

[10]

62. (a) Pollen tube ; 1

(b) One male nucleus fuses with egg cell / eq ;Forms zygote ; Which is {diploid / eq} ;One male nucleus fuses with {polar nuclei / fusion nucleus} ;Forms endosperm ; Which is {triploid / eq} ; 4

(c) (i) 21 to 22 (%) ; 1

(ii) {Rises / 21–24% figs. Given} from 10 to 15 % ;Reaches {a peak /eq} at 15 % ;Decreases from 15 to 25 % ; 2

[8]

63. (a) Stage Prophase I / metaphase I / diplotene /diakinesis;

Reason Chromosomes paired / bivalents present / synopsis ;

Reference to {chiasmata formation / crossing over} ; 3

(b) (i) 180 ;

(ii) 360 ; 2

(c) Halves the number of chromosomes /eq ;Reference to genetic variability / eq ;Diploid number restored at fertilisation / eq ; 2

[7]

64. (a) 4 ; 1

(b) B A D C E ;[correct sequence = 2 marks, one error = 1 mark] 2

33

(c) Halves chromosome number / diploid to haploid / 2n to n ;Diploid restored at fertilisation ;Reference to genetic variation ;Four {sperm / gametes} produced ;From each spermatogonium / eq ; 4

(d) Very few sperm reach the ovum / eq ;Reference to some sperm not motile / eq ;Therefore large number needed / eq ;Reference collective activity / eq ; 2

[9]

65. (a) (gene) {length / eq} of DNA that codes for {polypeptide / protein /eq};(allele) form of gene /eq ; 2

(b) (i) dominant ;if recessive not possible to produce child D or G,(as all offspringin second generation would have to be Dd)/eq explanation ; 2

Must use D and d(allow CE for other letters used in(b)(ii))

(ii) B – DdF – ddJ – Dd[ 2 correct = 1, 3 correct = 2 ] 2

(iii) 50% / 1 in 2 / 0.5 / ½ ;(parental genotypes) dd × Dd ;Clearly indicated gametes ;offspring genotypes /(at least Dd and dd) ; 3

(c) 1. mutation ;2. occurs during meiosis /suitable cause of mutation /ref to non-disjunction;3. causes faulty {protein /polypeptide/eq} to be produced /might not

be produced ;4. recessive/ both parents could be carriers /eq;5. offspring inherit recessive(allele) from both parents ; 2

[11]

34

66.

Starch Cellulose

Molecule with branchesattached by 1-6 linkages

Molecules always longand straight

Formed from α glucosemolecules

Form microfibrils byhydrogen bonding

Major component ofplant cell walls

Stored in amyloplasts

One mark for each correct row; ; ; ; ;

Empty box = no marks

[Reject ticks that might be crosses][5]

67. Meiosis;

Halved / ½;

Random(ly) / independently;

(Digestive) enzymes / lysozyme / eq;

Acrosome;

Zygote;

Mitosis;[7]

68. (a) (i) Mitochondrion / mitochondria;

(ii) Ribosomes / rough endoplasmic reticulum / RER;

(iv) Golgi body / golgi apparatus / smooth endoplasrnic reticulum / SER;

(v) Vacuole;

(vi) Centriole; 5

35

(b) A description to include two from:

1. pits contain plasmodesmata / pass through pits

2. (plasmodesmata) are strands of cytoplasm (which connect plant cells)

3. pits are holes through (cell) walls / thinning of wall / eq{Accept thinning of wall / eq]

4. {plasmodesmata / pits} allow [ / named appropriate substance}to pass between (plant) cells / eq; 2

(c) Any two from:

1. (prokaryotic cell) has no nuclear membrane (whilst a eukaryoticcell does) / DNA not enclosed in a {nuclear membrane / nucleus};

2. (prokaryotic cell) has circular chromosome (whereas eukaryoticcell has linear ones) / (prokaryotic cell) has single chromosomewhereas eukaryotic cells have {many / several});

3. (prokaryotic cells) do not have {mitochondria / ch / endoplasmicreticulum / golgi body / centriole / lysosomes / membranebound organelle / structure within cell) (whereas eukaryoticcells can have);

4. (prokaryotic cells) can have {plasmids / pili / slime} capsule(eukaryotic cells do not);[Reject flagellum]

5. (prokaryotic cells) are much smaller (than eukaryotic cells);

6. (prokaryotic cells) always have a cell wall (only someeukaryotic cells have cell wall);

[To gain a mark there must be no ambiguity about whether thecandidate is referring to a prokaryotic or eukaryotic cell] 2

[9]

69. (a) A suggestion an explanation to include:

1. to remove / separate the soft tissues from the fibres;

2. by microbial / bacterial decomposition / activity; 2

(b) A description to include four from:

1. measure samples of fibres to standardise (same length / width);

2. increasing range of suitable masses / eq;

3. record mass needed to break fibre or record force (if anewton meter used);

4. repeats for reliability;

5. one good safety precaution;

6. appropriate reference to calculation of cross sectioned area; 4

(c) A suggestion to include two from:

36

1. cotton has to be imported / eq;

2. Lower transport costs;[Accept other good reference to costs]

3. more expensive fertilisation / pesticides used to grow cottonor converse for nettles / grow any where / waste ground; 2

[8]

70. (a) (i) A description to include four from:

1. animals / cell culture tested for humans;

2. reference to female subjects;

3. (phase I) preliminary (small scale) tests on healthy volunteers;

4. {independent / official} body of {scientists / medics} /(UK) Medicines Control Agency decides whetherwork can progress (to phase 2);

5. (phase II drug tested on small groups of (volunteer){patients / people} who already have the disease;

6. (phase III) {larger / 1000 to 3000 group of} {patients / people}who already have the disease;[Accept if no reference to phase I and I]

7. placed randomly in two groups one to receive treatmentthe other not / as control;

8. one group given medical product the other a placebo /dummy treatment / no active ingredient;

9. (double blind test) neither patients nor doctors knowwho has the active compound;

10. statistics used to analyse results / test for significance;

[Credit points 6-9 in context of animal testing] 4

(ii) An explanation to include two from

1. only sick patients treated;

2. high risk doses / patients nearly died;

3. no placebo / control used / not a double blind test;

4. no control by regulatory body;

5. small sample size; 2

37

(b) In favour:

1. Relief of human suffering;

2. Cancer a very serious condition / causes death / severedistress / no satisfactory alternative way of treating it;

3. Debatable whether an embryonic stem ccli can be regardedas a potential human life but adult stem cells are not apotential human life;

4. Developing stem cell technology could lead to cures forother conditions;

5. Any balanced view an the use of stem cells;

[Level marking award points 1-4 to a max 2 marks and point 5 for the 3rd

mark]

against:

1. Stem cells can be harvested from human embryos /increases pressure to produce embryos specially for treating people;

2. Embryos have right to life / use at embryos = murder;

3. Research using non-embryonic stems could make use ofembryonic stem cells unnecessary;

4. Could be unforeseen side effects for the woman / anychildren she has / correct reference to gene line /might lead to even more ethically questionable practices;

5. Any balanced view on the use at stem cells;

[Level marking award points 1-4 to a max 2 marks and point 5 for the 3rd mark]

[A candidate who does not express a position can only be awarded amaximum of two marks unless he or she has deliberately chosen andattempted to justify an undecided position supported by an argumentthat the ethical issues are so finely balanced that he or she wouldnot like to come down on either side] 3

[9]

71. (a) An explanation to include two from:

1. Biodiversity depends on number of species;Reject ‘amount’

2. (Extinction) reduces this;

3. Dependent species affected; 2

(b) (i) Source of protein / source of energy / reference to proteinsynthesis / growth / few suitable alternative protein sources /reference to economic significance; 1

38

(ii) (A suggestion to include two from:

1. Smaller catch;

2. For African fishermen;

3. Fat bush meat instead / eq;

4. Correct reference to aquatic mammals; 2

(c) A description to include two from:

1. People will not change way of life easily;

2. Like European fishermen;

3. So unexpected effects;

4. Elsewhere;

5. African culture or using bush meat / eq 2

(d) An explanation to include three from:

1. Cannot control external factors;

2. Which might affect local area;

3. Could send problem elsewhere;

4. Conflicting needs not considered;

5. Reference to globalisation of human activities;

6. Wild populations not confined (to human boundaries);

7. Law of the commons / eq;

8. International agreements carry more weight / eq; 3[10]

72. 1. Centrioles;

2. Nucleolus;

3. Golgi (apparatus / body);

4. Lysosomes;[4]

39

73.

Structure Bacterial cell Liver cell

Ribosomes

Centrioles

Starch grains

Nucleus

(1 mark for two correct boxes)

Blank spaces are incorrect.A tick which has been crossed through and is ambiguous is incorrect.

[4]

74. (a) A = cisterna / cisternae;

B = (Golgi / secretory) vesicle / lysosome; 2

(b) 1. {modified / ref. to attachment (of another molecule)} (of protein);

2. carbohydrate / glycoside / (oligo)saccharide (chain) / to formglycoproteins;

3. (proteins) concentrated / eq;

4. idea that proteins end up in vesicles / within a membrane / lysosome; 3[5]

75. (a) acetic orcein / Schiffs / Feulgens / acetocarmine / lactopropionic acid /toluidine blue; 1

(b) prophase, telophase, metaphase and anaphase; 1

(c) (i) 1. idea that P1 is earlier (in prophase) than P2;

2. {chromosomes / threads / chromatids} can be seen(more) clearly / eq;

3. because (chromosomes / DNA) {shorten / spiral /condense / coil};

4. idea of chromosomes spreading out more;

5. ref to effect of preparation technique; 3

(ii) correctly labelled cell;

IF two cells are labelled, both must be correct 1

40

(iii) 1. centromeres divide / split / separate / pulled apart;

2. {spindle fibres / microtubules} become {shorter / contract /condense};

3. chromatids {separate / pulled apart};

4. chromosomes / chromatids move towards (opposite){poles / ends / sides / centrioles}; 2

[8]

76. (a) (i) spermatids; 1

(ii) spermatogonia / spermatogonium;

primary spermatocytes / primary spermatocyte; 2

(b) 1. meiosis / reduction division;

2. reference to halving the number of chromosomes;

3. idea that {the diploid number / 2n} restored at fertilisation / eq; 3[6]

77. (a) adaptations that enable a plant to {live in dry conditions / eq} /{reduce water loss / reduce transpiration }; 1

(b) 1. leaf is rolled / curled up / eq;

2. to reduce (exposed) surface area;

3. encloses stomata (on the inside);

4. presence of spines / hairs / spikes;

5. to trap air / trap humid air / trap moisture;

6. reduces the {diffusion / concentration} gradient;

7. thick cuticle;

8. any reference to reducing {transpiration / evaporation / water loss};

9. presence of hinge cells;

10. idea that hinge cells roll the leaf; 4[5]

41

78. (a) 1. as the concentration of garlic increases up to 60 – 80%{the growth of bacteria {decreases / inhibited} / more bacteria killed};

2. decrease in growth is proportional to increase in extractconcentration between 20% and 60%;

3. idea that a concentration of 60 - 80% (and over) has maximumeffect /eq; 2

(b) (i) Gram negative bacteria are affected; 1

(ii) idea of extract affecting gram negative bacteria more than itaffects positive bacteria / eq; 1

[4]

42

79. ESSAY MARK SCHEME

Outline scheme for marking essay

11 available for Scientific content (S)2 available for Balance (B)2 available for Coherence (C)


Description

11(good)

The essay demonstrates a sound understanding of the topic and contains a significant amount of material from most areas of the mark scheme, including A2 content.Suitable examples are included and the candidate has clearly and coherently linked together information from different parts of the specification.

9(above

average)

An above average essay, with accurate content. The essay includes a good balance of material from several areas of the mark scheme, including A2 content, and examples where appropriate.There may be some minor factual errors.

7(average)

The essay includes relevant information from some areas of the mark scheme, including A2 content. The candidate links together some facts and principles.Some examples are included.There may be some minor factual errors.

5(below

average)

The essay includes some generally factually accurate and relevant material, and there is some attempt to link material from more than one area of the mark scheme. The A2 content, in particular, lacks depth and accurate details.

3(poor)

There are some correct facts, but the essay lacks depth and accuracy. The essay contains little or no relevant information from the A2 content.

1(poor)


0(poor)

No correct or relevant material is included.


An essay containing AS content only can be awarded a max of 3 for scientific content.

An essay containing A2 content only can be awarded a max of 7 for scientific content.S = 11 marks

43

Balance (B)


1. Some of the main topic areas outlined are covered.Some discussion of each of the areas chosen.Some irrelevant material included.There are some examples which link together different areas of the specification.Some errors


B = 2 marks

Coherence (C)




C = 2 marks

44

[A2 content is in bold]

Introduction could include ref to the importance of sexual reproduction giving rise to genetic variation –

Gamete formation involves meiosis – independent assortment

Crossing over –

Random fertilisation –

Mutations giving rise to genetic variation –

Selection pressures act on the gene pool –

Changes in allele frequency in populations –

Stabilising, directional and disruptive selection –

Natural selection giving rise to speciation –

Allopatric speciation –Sympatric speciation

Scientific content 11 marksBalance 2 marks

Coherence 2 marks[15]

80.

Feature Sperm Egg

Tail

(i) Haploid nucleus

(ii) Acrosome present

(iii) Mitochondria present

(iv)Cytoplasm containingmany lipid granules

(v) Use ATP for movement

(1) per line

NB an empty box = (0) for that linea tick/cross hybrid = (0) for that line

[5]

81. (a) (i) onion / garlic / other suitable species;

(ii) root tip; 2

(b) (acidic/acidified/acetic/ethanoic/propanoic) orcein / feulgen / toluidene blue; 1

45

(c) to macerate them/to separate the cells; 1

(d) A = centromere;B = chromatids; 1

[6]

82. (a) (i) (superovulation) from IVF treatment; 1

(ii) totipotent cells can give rise to a complete human/all cell types;pluripotent can only give some cell types; 2

(b) (i) cells allowed to multiply / produce more cells;in petri dish/test tube / any reasonable attempt to refer to suitableculture vessel;reference to culture medium/incubator/sterile conditions;to produce more (identical) cells; 2

(ii) cell becomes specialised (in function)/stem cells develop intodifferent types of cells;cells stop dividing;one type of cell can be used to produce a specific type of tissue /named example;one cell type can be sued to produce tissue / use of named example; 2

(c) This question is intended to test the candidate’s ability to deal thoughtfullywith a moral dilemma and to balance scientific knowledge and ethicalconsiderations. These are the kinds of skills developed throughwell-informed class discussion.

Candidates must decide for or against - a candidate who does notmake his or her choice clear is limited to a maximum of 3 marks.

A candidate who presents points for and against without expressingan opinion is limited to a maximum of 3 marks for valid pointseither for or against (which ever is the greater) unless he or shepresents a good case why the matter is too finely balanced to comedown one way or the other.

To gain 4 marks a candidate must include one of the points markedwith an asterisk in the mark scheme which attempts to counter theopposing view.

46

Against:• Embryonic stem cells are (potential) people/babies;• From the moment of conception;• Objectional on religious/ethical grounds; [do NOT credit unqualified

statements such as ‘unnatural’, against nature’ ‘playing God’]• Pressure on women to produce surplus embryos;• Cloning/stem cell techniques may get into the wrong

hands/regulation might be difficult to police* / might be thethin edge of a wedge like designer babies;

• It will soon be possible to use non-embryonic stem cells soresearch into the use of embryonic stein cells is unnecessary / eq; (*)

• Although there are some advantages there could be unexpecteddangerous consequences therefore not worth the risk / eq; (*)

For:• Potential for alleviating human suffering / eq(*);• Specific example e.g. culturing patient’s own cells to provide

replacement tissues/organs;• Stem cells from IVF would otherwise be discarded;• Embryos should not be considered as human at an early

stage (awareness that only cells at a very early stage are used) (*).• Use of non-embryonic cells will need a development phase

using embryonic cells / more can be done with embryonic stem cells;• Ethically questionable to use embryonic stem cells but these

objections are outweighed by the greater evil of not usingembryonic stein cells to alleviate human suffering (*),

• Could be excesses but these can be regulated (*); 4[11]

83. (a) proportion of total alleles;for one gene (in a population)/eq; 2

(b) different alleles exist / ref mutation;advantage in specific environment;ref selection pressure;more likely to reproduce;allele passed to offspring more often;ref at disadvantage in other environment;

Allow converse argument 4

(c) faster life cycle of bacteria/converse/ eq;greater selection pressures on bacteria (eg antibiotic use);ref plasmid transfer in bacteria/eq;larger numbers of bacteria hence larger gene pool/eq;ref. mutation; 2

[8]

47

heading 6;heading 7;heading 8;heading 9;ex;ex2;graph;Default;VertQuallevel;Monthyear;Prodname;Quallevel;Subref;Docucontent;g-text;text;Multi-Choice Misctext;Examiner's Report;Title;Subtitle;header;Normal (Web);Hyperlink;right;accept;84.

Breadth: maximum of 6 marksThese marks are to be awarded to the candidate if they successfully introduce the general area of Biology relevant to the essay title. If a relevant B point is awarded then the corresponding A point should also be awarded. Key ideas to look for are in bold type – the candidate need only show evidence that he or she realises that key idea is appropriate in the essay to gain a breadth (A) mark.

Depth: maximum of 8 marksThese marks are awarded to candidates for demonstrating an understanding of relevant A level biological detail expanding on the areas of biology introduced in A. This list is not exhaustive but is designed to give an idea of the type of response worthy of credit for a (B) mark. Allow a maximum of 4 B marks per corresponding A mark.

A1 Description of Stem Cells: B1a

B1b

Cells that are able to differentiate into more than one cell type/eq;Correct descriptions making use of the words totipotent, pluripotent and/or multipotent;

B1c

B1d

Reference to cell/ nuclear division as source of new cells;Good description of mitosis and/or cell cycle including details such as the names of the phases;

B1e

B1f/g

Introduction of concept that cells specialise during their development;Good description of gene switching/induction/inactivation such as the use of transcription factors/methylation [2 marks available for excellent description including 2 methods of specialisation]

A2 Source of embryonic stem cells: B2aB2b

IVF as a source of spare embryos;Details of how IVF tends to produce excess embryos and that those embryos may be stored for long periods in liquid nitrogen.

48

B2c

B2d

Cloning to produce embryonic stem cells;Details of a suitable cloning technique; e.g. description of how Dolly was cloned

A3 Other sources of stem cells: B3a

B3b

Coral blood (from placenta/umbilical cord);Explanation that placenta/umbilical cord contains stem cells that will be identical to the new born child and they may be harvested and stored or used.

B3cB3d

Adult stem cells;Example of tissue that contains stem cells e.g. bone marrow, testes, etc

A4 Therapeutic uses of Stem cells B4a/b Credit two specific examples of a tissue/organ that could be replaced/healed through the use of stem cells e.g. repairing spinal cord injuries

A5 Cloned/Adult stem cells are less likely to be rejected by the patient

B5a Details of the specific immune system and reasons why traditional transplants may be rejected

B5b Details of why cloned cells are not going to be rejected by the immune system e.g. ref to antigens/MHCs etc.

B5c No need to use immune suppressant drugs with stem cells/converse.

A6 Adult stem cells will need to be reprogrammed

B6 Use of chemical signals to enable stem cells to differentiate to produce the desired cell types.

A7 Stem cells can be manipulated by gene therapy

B7a Details of how to insert a gene into a stem cell

B7b Description of a suitable vector e.g. liposome, retrovirus, etc

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B7c Example of specific disorder/disease that could be treated through gene therapy e.g. cystic fibrosis, diabetes, SCID etc

B7d Further detailed explanation of the case study named in B7c e.g. replace gene for insulin production into pancreatic stem cells and stimulate them into becoming Islet cells

A8 Alternatives to the use of stem cells

B8aB8b

Xenotransplantation.Details and examples e.g. heart valves from pigs

B8c Dangers of xenotransplantation e.g. new viruses become active/ or need for genetic modification of the animal so that it is not rejected by the immune system

B8dB8e

Prosthetic replacementsSpecific example e.g. artificial heart valves or hearts, limbs

A9 Ethical Issues B9aB9b

eugenicsIssues described related to selection of embryos, designer babies etc through genetic modification

B9cB9d

Pro-life issuesDiscussion about embryos having the potential for independent life in the future – should we be allowed to manipulate/destroy

B9eB9f

Technology may be misusedOnce therapeutic cloning is possible others will use the technology for reproductive cloning or similar.

A10 Dangers/Disadvantages B10aB10b

Developmental deformities/CancersExplanation linked to cells not being fully reprogrammed/ new mutations/

B10cB10d

Premature aging of cells/organismChromosomes come from an older donor nucleus – shorter telomeres etc.

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Unpacking the question: The C points might be made as discrete points in the introduction and/or conclusion or indirectly as part of the way the factual material has been presented in the body of the essay. But it should be possible to identify precisely where each C mark has been awarded by, for example, writing C1 or C2 on the script.

C1 Recognition that embryonic stem cells have more potential than adult stem cells but they raise more ethical issues regarding their use.

C2 An issue of balancing risks and benefits for any new therapies.

C3 Adult stem cells will not need to be cloned, but will need to be reprogrammed and may be harder to extract.

C4 Issue of whether it is better to make use of spare embryos resulting from IVF rather than disposing of them.

C5 Essay provides a balanced argument that includes at least 2 good examples of the use of stem cells and 1 danger/ethical problem associated with the use of stem cells.

C6 Discussion of how the human genome project has helped identify candidate genes for gene therapy.

C7 Evidence that candidate is aware of the key issues of needing to understand the precise series of chemical signals required for cells to specialise successfully and form the correct tissues/organs required.

C8 reference to the role of clear legislation/supervision of work in these key areas e.g. outline of the role of the Human Fertilisation and Embryology Authority (HFEA).

C9 Recognition that stem cells may be cultured and manipulated in tissue culture before use/storage

C10 Need for greater research/understanding careful testing before proceeding with new therapies

C11 Key question is about the status of the embryo – a ball of undifferentiated cells or a potential human being.

C12 Tissue typing may reduce need for cloning as we may only need a few stem cell lines to avoid tissue rejection in most people.

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D: Coherence, clarity and expression of the answer:maximum of 4 marks

This strand will award students for style of their answer and is quite distinct from mentioning the big ideas (C). It isn’t what candidates say but how they say it.

4 marks: A truly synoptic essay which links together information from different parts of the specification in a coherent and logical style (introduction. Conclusion, good use of paragraphs and well illustrated by examples). Good spelling, punctuation, grammar and sound use of technical terminology.3 marks: Good logical structure with good spelling, punctuation, grammar and sound use of technical terminology, but tends to be a collection of information which, although relevant, tends to be disjointed and only partly attempts to synthesise information.2 marks: A reasonably coherent account that includes satisfactory spelling, punctuation and grammar, which tends to be disjointed. A collection of information with little or no attempt to link ideas together.1 mark: Some relevant information is presented in an intelligible way using correctly formulated simple sentences.0 marks: The use of English is not adequate to convey scientific information beyond naming a list of examples. A candidate who has scored some marks (particularly in strand A) for mentioning some relevant points may nevertheless fail to score marks in strand D if he or she fails to form simple sentences.

[20]

85. (a) (i) cell in anaphase correctly identified; 1

(ii) cell in telophase correctly identified; 1

(iii) 2 / 3; 1

(b) 1. idea that during prophase {chromosomes / chromatids}(becoming) visible;

2. idea of centrioles move to opposite poles;

3. reference to formation of {spindle /spindle-fibres / microtubules};

4. disappearance of nucleolus / nucleoli;

5. breaking down of nuclear {envelope / membrane} (in prophase) ornuclear envelope is broken down by metaphase / eq;

6. (at metaphase) {chromosomes / centromeres} attached to spindle(fibres);

7. idea of {chromosomes / chromatids} lined up at equator; max 5[8]

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86. (a) 1. {envelope / double membrane} clearly shown;

2. granum clearly shown;

3. {granum / thylakoid(s)} labelled;

4. {stroma / ribosomes / starch grain / DNA / lipid droplet / {double/ inner / outer} membrane / envelope / intergranal lamellae}correctly labelled; 4

(b) (i) 1. correct length;

2. divided by 50 000;

3. correct length in µm; 3

(ii) vacuoles / vesicles / lysosomes / glycogen granules / ribosomes /lipid droplets / centrioles / spindle fibre / microtubules; 1

(iii) {resolution not high enough / eq} / damage / {angle of section /eq} / {poor printing of photograph / eq}; 1

[9]

87. (a) (i) 1. presence of gills;

2. to increase surface area / increase uptake of oxygen;

3. presence of haemoglobin / respiratory pigment;

4. with high affinity for oxygen;

5. presence of siphon / (breathing) tube / eq;

6. to obtain oxygen (directly) from the air;

NB paired points max 4

(ii) 1. presence of claws / hooks / suckers;

2. to attach to substrate / eq;

3. {flattened / streamlined / eq} body /reference to burrowing;

4. less resistance to water flow / less likely to be washed away;

NB paired points max 2

(b) 1. inverse relationship / eq;

2. credit a manipulated quantitative comment; 2[8]

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88. (a) E D C B A;;

NB All correct = 2 marks, 1 error (i.e. one letter out of sequence) = 1 mark 2

(b) (i) 46;

(ii) 23; 2

(c) 1. {primordial (germ) cells / oogonia} divide by mitosis;

2. oogonia (develop to) form primary oocytes;

3. primary oocytes divide by meiosis I;

4. to form a secondary oocyte;

5. and a polar body;

6. secondary oocyte divides by meiosis II;

7. to form an ovum; max 4[8]

89.

Name of cellstructure

Description of cellstructure

Diagram of cellstructure

nucleolus;

(1)

pair of cylinders;

at right angles toeach other;

(2)

1. spherical (structures);

2. single membrane;

3. containing{hydrolytic / eq}enzymes;

max (2)

microtubules;

(1)

[6]

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90. (a) 1. cell cycle is shorter in A than B /eq;

2. {interphase / eq} is shorter in A than B / eq;

3. {mitosis / eq} is shorter in A than B / eq;

4. {S phase / eq} is the same duration;

5. comparative figures; max 3

(b) 1. cells preparing to divide /eq;

2. reference to S phase;

3. reference to replication (of DNA);

4. reference to semi-conservative (replication) or adescription of it;

5. idea that new cells will have same quantity of DNA asparent / eq; max 2

(c) 1. chromosomes {move to / at} opposite poles of cell / eq;

2. reference to formation of nucleus / eq;

3. reference to formation of cell {plate / wall};

4. {cell splits in two / eq} / reference to cytokinesis; max 2[7]

91. (a) 1. thick cuticle;

2. reduces {transpiration / water loss / eq};

3. leaves rolled / folded / curled up / eq;

4. reduces (exposed) surface area / stomata enclosed /reduces air movements / eq;

5. sunken / fewer stomata;

6. reduces {transpiration / water loss / eq};

7. presence of spines / spikes / hairs;

8. trap water vapour near leaf / reduces air movement / eq;

9. reference to hinge cells;

10. (which) cause the leaf to roll up / eq; max 6

(b) leaf not rolled / no hairs / no spines / thin cuticle / no cuticle/ air spaces / aerenchyma / no stomata / stomata on upperepidermis only / stomata on upper surface only / lesssupporting tissue / stomata not sunken / leaves feathery / eq; 1

[7]

92. ESSAY MARK SCHEME

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Outline scheme for marking essay

11 available for Scientific content (S)2 available for Balance (B)2 available for Coherence (C)


Description

11(good)

The essay demonstrates a sound understanding of the topic and contains a significant amount of material from most areas of the mark scheme, including A2 content.Suitable examples are included and the candidate has clearly and coherently linked together information from different parts of the specification.

9(above

average)

An above average essay, with accurate content. The essay includes a good balance of material from several areas of the mark scheme, including A2 content, and examples where appropriate.There may be some minor factual errors.

7(average)

The essay includes relevant information from some areas of the mark scheme, including A2 content. The candidate links together some facts and principles.Some examples are included.There may be some minor factual errors.

5(below

average)

The essay includes some generally factually accurate and relevant material, and there is some attempt to link material from more than one area of the mark scheme. The A2 content, in particular, lacks depth and accurate details.

3(poor)

There are some correct facts, but the essay lacks depth and accuracy. The essay contains little or no relevant information from the A2 content.

1(poor)


0(poor)

No correct or relevant material is included.


An essay containing AS content only can be awarded a max of 3 for scientific content.

An essay containing A2 content only can be awarded a max of 7 for scientific content.S = 11 marks

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Balance (B)


1. Some of the main topic areas outlined are covered.Some discussion of each of the areas chosen.Some irrelevant material included.There are some examples which link together different areas of the specification.Some errors


B = 2 marks

Coherence (C)




C = 2 marks

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Sexual reproduction in flowering plants and genetic variation

introduction could include reference to sexual reproduction involving the fusion of gametes, leading to genetic variation

AS structure and functions of the principal parts of a flower –

pollination –

adaptations to insect pollination –

adaptations to wind pollination –

events leading to fertilisation –

mechanisms for ensuring cross-pollination –

A2 continuous and discontinuous variation –

meiosis as a source of genetic variation –

random fertilisation –

mutations –Scientific content 11 marks

Balance 2 marksCoherence 2 marks

[15]

93.

Plant (eukaryotic) cell

Animal (eukaryotic) cell

Bacterial (prokaryotic) cell

Cell wall ;

Chloroplasts

Nuclearmembrane

;

Cell (unit) membrane

;

Ribosomes ;

Centrioles ;

max 5[5]

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94. 1. insulin detaches from ribosomes / rough endoplasmic reticulum / RER;

2. (insulin) passes through / inside endoplasmic reticulum(to golgi body);

3. (insulin) passes from endoplasmic reticulum to golgibody in vesicles;

4. (insulin) assumes 3-D shape whilst passing through ER;

5. (insulin) is (further) modified inside golgi body;

6. (insulin) is enclosed in vesicles budded off / produced by golgi body;

7. vesicles fuse / join with cell membrane (releasinginsulin to exterior);

8. (insulin passes through cell membrane) by exocytosis; max 5[5]

95. (a) 1. cellulose has β-, starch has α-glucose;

2. cellulose has unbranched, starch can have branchedmolecules;

3. cellulose molecules are much longer / several thousand(glucose) molecules long whilst starch several hundred;

4. cellulose molecules are straight, starch molecules arecoiled / spiral;

5. cellulose molecules are only of one type, starch can bea mixture of two types of molecules / amylose andamylopectin;

6. cellulose only has 1 – 4 glycosidic bonds whilst starchhas 1 – 4 and 1 – 6 glycosidic bonds; max 3

(b) 1. (cellulose) molecules parallel / side by side;

2. joined by hydrogen bonding; 2

(c) 1. (cohesion is) the attraction between like molecules /water molecules (tendency) to stick together / eq;

2. by hydrogen bonding;

3. appropriate references to polarity of water molecules; max 2[7]

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96. (a) 1. halves the chromosome number / one of each pair ingamete / haploid cells;

2. randomly assorts the chromosomes / genes;

3. provides genetic variation;

4. the diploid number is maintained (in the zygote); max 2

(b) 1. acrosome present;

2. digestive enzymes / eq;

3. breakdown jelly surrounding ovum / allow head toreach the ovum membrane;

4. reference to genetic material passing through ovum membrane; max 2

(c) (i) 16; 1

(ii) the cells do not {grow / increase in volume} / no newcytoplasm is produced; 1

(iii) 1. chromosomes {shorten / coil} / condenses / becomevisible;

2. (each chromosome becomes visible) as two chromatids;

3. nuclear membrane / envelope breaks down;

4. centrioles position themselves at opposite end of thecell / eq;

5. spindles formed from microtubules / between {poles /centrioles}/ eq;

6. chromosomes on the equator / eq;

7. {attached / eq} by centromeres; max 3[9]

97. (a) (ii) 1. {not all / different} genes are switched {on / off} /active / activated;

2. correct and appropriate reference to factors /mechanisms for gene switching;

3. e.g. reference to promoters / transcription factors; max 2

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(iii) 1. if you (suffered an accident / disease / deterioration)and needed to replace damaged brain cells;

2. would be genetically the same as the rest of your cells;

3. able to replace more than one kind of brain cell;

4. goes on generating new cells as required / eq; max 2

(b) (i) 1. embryonic cells are easier to work with than adult stemcells;

2. embryonic cells are (relatively) undifferentiatedwhereas adult stem cells {are/appear to be} less so;

3. embryonic stem cells are {totipotent / pluripotent /able to become any kind of cell in the body}, but adultstem cells are {multipotent / able to become only alimited number of cell types};

4. embryonic stem cells have a wider range of clinicalapplications / adult stem cells have a narrower range ofclinical applications; max 2

(ii) AgainstCredit any three of the points below:

1. embryonic stem cells (are taken from embryos) which(are to be considered) unborn children / eq;

2. use of stem cells is thus effectively murder / lack ofrespect for embryo as a (potential) human;

3. a lot of current (embryonic) stem cell treatment isfraudulent / badly regulated / exploits suffering /encourages IVF clinics to ‘create’ more ‘spare’embryos;

4. if we wait a few years longer we shall have the samebenefits through adult stem cells;

5. not enough funding for alternatives e.g. adult stem cells;

6. an embryo becomes a new human at the moment ofconception / eq;

The fourth mark: for attempting to balance opposing points ofview whilst thoughtfully coming down on one side e.g.“Even though it may benefit people this does not justify takingthe life of an unborn child”;

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ForCredit any three of the points below:

1. offers prospect of treatment to many suffering people;

2. research using alternatives e.g. adult stem cellsprogressing more slowly than that with embryonic stemcells;

3. if we ban it in the UK it’ll still happen in other countries;

4. using spare IVF embryo which would alternatively bedestroyed;

5. research with embryonic stem cells is needed todevelop use of adult stem cells;

6. an embryo is not a new human until it is viable / eq;

The fourth mark: for attempting to balance opposing points ofview whilst thoughtfully coming down on one side e.g.“Alleviation of suffering in people (who have already beenborn) is (ethically) more important than destroying embryos”; max 4

[11]

98. (a) (i) B; 1

(ii) Spindle fibre;

Accept Spindle 1

(iii) Metaphase;

Accept Metaphase I 1

(b) Award one mark for each of the following points in context to amaximum of four marks.

1. Ref. to use of root tip;

2. Add {acid / named acid / acetic alcohol};

3. Add appropriate named stain e.g. toluidine blue, aceticorcein, Schiff’s reagent, Feulgen’s reagent;

4. Break open tip with {(mounted) needle/eq};

5. Mount in {stain / acid / water};

6. (Gently) squash under coverslip;

7. Warm (to intensify staining); 4[7]

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99. (a) (i) Award one mark for each of the following points in context.

1. ref. to random aligning of chromosomes/eq;

2. idea of new combinations of {(parental) chromosomes /alleles}; 2

(ii) Award one mark for each of the following points in context toa maximum of two marks.

1. breaking and rejoining of {chromatids / DNA /eq};

2. on same chromosome pair;

3. recombines {genes / alleles} / produces recombinants /eq; 2

(b) Award one mark for each of the following points in context toa maximum of two marks.

1. Height increased (from 1950) until 1970;

2. Plateau /eq (after 1970);

3. Relevant correct manipulation of data from graph; 2

(c) Award one mark for each of the following points in context toa maximum of three marks for each section, and a maximumof four marks overall.

Environmental

1. Diet is an environmental factor;

2. Protein content increases;

3. Protein required for growth;

4. This leads to increase in height up to 1970;

Genetic

1. {Plateau / level off} in height (after 1970);

2. indicates a (potential) maximum height/eq;

3. this is a genetic factor;

4. no change in height despite further protein increase (after 1970); 4[10]

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100. (a)

Organelle A B C D E

Rough endoplasmic reticulum

Mitochondrion

Golgi apparatus

3

(b) Award one mark for each of the following points in context to amaximum of three marks.

1. {layers / stacks} of {membrane / cisternae};

2. single membrane;

3. similar to endoplasmic reticulum;

4. difficulty interpreting electron micrographs;

5. reference to {limited microscope techniques /artefacts / resolution}; 3

(c) (i) Award one mark for each of the following points in context.

1. idea of different levels of radioactivity from other organelles;

2. peak at different time; 2

(ii) Award one mark for each of the following points in context toa maximum of four marks.

1. radiactivity peaks first in RER;

2. protein synthesised (in RER);

3. vesicles containing protein formed by RER;

4. vesicles migrate and fuse to Golgi;

5. which is where the second peak;

6. protein modified in Golgi;

7. vesicles (containing protein) formed from Golgi;

8. third peak in secretoty vesicles;

9. (vesicles contain protein) for secretion; 4

(iii) Award one mark for one of the following points only.

1. Background/eq;

2. Amino acids diffuse in mitochondria;

3. Radioactive protein {used by / found in} mitochondria; 1[13]

101. (a) Acrosome 1

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Flagellum 1Accept Tail

Mitochondria 1Reject midpiece

(b) Totipotent

Accept totipotency

Reject pluripotent 1

(c) Award one mark for each of the following points in context toa maximum of three marks.

1. some genes active / some genes inactivated;

2. only get mRNA from active genes;

3. active mRNA translated to specific protein;

4. proteins modify cell;

5. changes permanent/difficult to reverse;

6. ref. to differentiation; 3

(d) Award one mark for each of the following points in context toa maximum of three marks.

1. {these / unfertilised} embryos not viable;

2. objections to discarding viable embryos / no objectionto discarding non-viable embryos;

3. rights from moment of fertilization;as they are genetically unique/eq; 3

[10]

102. (a) Award one mark for one of the following points only.

1. binomial name is unique;

2. more precise / less confusion than simple names; 1

(b) Class = MammaliaReject any mis-spelt answers

Order = Cetacea

Family = Balaenopteridae

All three correct = 1 mark 1

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(c) A;

B;

in A, B and C / D = 1 mark in A / B and C and D = 0 marks in A, B, C and D = 0 marks 2

(d) Award one mark for each of the following points in context to amaximum of three marks.

1. idea that they are very similar / share many {features/eq};

2. reference to homologous features;

3. in structure / behaviour/eq;

4. idea that they cannot breed together;

5. to produce {fertile / sexually viable} offspring; 3[7]

103. (a) The number of (different) species in a {habitat /environment / ecosystem/eq}; 1

(b) Award one mark for each of the following points in context toa maximum of three marks.

1. both have decreased;

2. decrease in roadside verges greater than in hedgrows;

3. {percentage / proportional} decrease greater in roadsideverges greater than in hedgerows;

4. roadside verges greater species richness in 1990 and in 1998;

5. correct manipulation of figures to quantify any comparison; 3

(c) Award one mark for each of the following points in context toa maximum of three marks.

1. idea that species richness gives no indication ofabundance of each species;

2. idea that biodiversity refers to {variety/eq} of organisms;

3. ref to use of a calculated biodiversity index eg Simpson’s;

4. using species richness value / number of different species;

5. number of individuals in each species recorded;

6. ref to genetic diversity; 3

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(d) Award one mark for each of the following points in context toa maximum of five marks.

1. reference to seeds stored in cool, dry conditions;

2. seeds can be stored for {long time/eq};

3. {viability tests/eq} carried out at regular intervals;

4. {more economic / less costly / less labour involved} thanconserving {living plants/eq};

5. less space needed/eq;

6. {large numbers/eq} of plants can be stored;

7. seeds do not need be stored in original {habitat/eq};

8. less likely to be damaged by {vandalism / natural disaster/eq};

9. less likely to be damaged by {disease / herbivores/eq};

10. ref to any other valid comment about the value ofconserving plant species; 5

[12]

104. (a) (i) 287; 1

(ii) 287 / 1432 or relevant working;20 / 20.0;

[Allow consequential error from part (i)] 2

(b) Award one mark for each of the following points in context toa maximum of two marks.

1. biodegradable;

2. use renewable material;

3. sisal {obtainable / grown} {easily / locally / similar idea};

4. fibres extraction more suited to {developing countries /small scale};

5. cheaper;

6. less use of fossil fuel/eq;

Assume idea relates to sisal unless stated otherwise, butaccept converse arguments for nylon. 2

(c) (i) Ability to resist {stretching / being broken when pulled} /maximum {load / force} which can be applied before breaking; 1

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(ii) Award one mark for each of the following points in context toa maximum of four marks.

1. idea of suspending {fibres / bundles of fibres} withweights on / pulling them with a forcemeter/eq;

2. {fibres / bundles of fibres} of same diameter used /different diameters accounted for;

3. {fibres / bundles of fibres} of same initial length used;

4. detail of how {weights added / forcemeter pulled};

5. description of measurable endpoint eg {breaking point /stretched to standard length};

6. repeated readings taken at each {weight / forcemeterreading} (using different fibre NOT just checking thereading with same fibre);

7. reference to a safety procedure eg {goggles in case fibresnaps / precaution against falling weights};

8. ref to control of {temperature / humidity / otherrelevant factor}; 4

(d) Award one mark for each of the following points in context toa maximum of two marks.

1. lignin in wall / lignified walls;

2. reference to {thick / thickened} walls;

3. dead / no living contents / hollow lumen;

4. elongated / much longer than they are wide; 2[12]

105. (a) A;

C;

in A, B and C / D = 1 mark in A / B and C and D = 0 marks in A, B, C and D = 0 marks 2

(b) 1. = mitochondrion;

2. = amyloplast;

3. = lysosome;

Reject any other answers 3

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(c) Award one mark for each of the following points in context toa maximum of four marks.

1. cellulose molecule is an unbranched {polymer/chain};

2. of β-glucose;

3. joined by glycosidic bonds;

4. microfibril formed from 50 to 80 cellulose molecules;

5. reference to hydrogen bonds (between adjacentcellulose molecules);

6. between adjacent –OH groups;

7. large number of hydrogen bonds; 4[9]

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Bio Unit 2 All Topics Answers

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