SAJC 2007 H2-Bio-TYS-ANS

2007 ‘A’ Level H2 Biology Mark Scheme (updated 10 Jan 2015) 1 2007 ‘A’ Level H2 Biology Mark Scheme PAPER 1 (MCQ) 1 C 21 B 2 B 22 C 3 B 23 D 4 C 24 A 5 B 25 D 6 D 26 A 7 B 27 C 8 C 28 D 9 B 29 D 10 C 30 C 11 D 31 B 12 A 32 D 13 C 33 A 14 A 34 C 15 A 35 D 16 D 36 A 17 C 37 C 18 C 38 A 19 D 39 D 20 C 40 D

2007 ‘A’ Level H2 Biology Mark Scheme (updated 10 Jan 2015) 2 PAPER 2 (CORE) QUESTION 1 (a) A – viral RNA B – reverse transcriptase C – capsid protein (b) 1 host cell surface membrane surrounds virus particle / (viral) RNA and protein; 2 ref. synthesis of surface glycoprotein; 3 budding; R exocytosis (c) (i) 1 block protease active site so that substrate unable to bind; 2 viral polyprotein not cut / structural / enzyme protein not formed; 3 (newly formed) virus unable to infect further cells; (ii) 1 similar shape to polyprotein / complementary shape to active site; 2 inhibitor not hydrolysed so remains in active site; QUESTION 2 (a) 1 fluid refers to the phospholipids and proteins being free to move; 2 phospholipids also being able to move within a layer, transversely; 3 mosaic refers to the proteins embedded in the phospholipid bilayer, where they are scattered; (b) (i) 1 glucose is a polar molecule and ions are charged; 2 unable to pass through hydrophobic region within the membrane; 3 ref. to specificity of transport proteins;

2007 ‘A’ Level H2 Biology Mark Scheme (updated 10 Jan 2015) 3 (ii) 1 high levels of ATP close ATP-sensitive potassium channels; 2 build up of potassium ions inside cell; 3 depolarize membrane; (iii) 1 insulin release involved exocytosis and therefore did not require a protein channel; 2 insulin is a protein; 3 too large to pass through membrane; 4 ref. to channel large enough to allow insulin through would allow other molecules through; (c) 1 vesicles containing insulin move to cell surface membrane; 2 membrane of vesicle fuses with cell surface membrane; 3 vesicle contents emptied by exocytosis; QUESTION 3 (a) 1 DNA strands separate by hydrogen bonds breaking; 2 both strands act as templates; 3 each new molecule of DNA contains one new and one original strand of DNA; (b) 1 ref. to shape of active site of DNA polymerase; 2 needs 3’OH to initiate action of DNA polymease; 3 primers add only at 3’; (c) 1 DNA in bacteria occurs in a loop while human DNA is linear; 2 bacteria DNA is naked while human DNA is arranged in nucleosomes wrapped around histones; 3 ref. to introns only in human DNA; 4 ref. to telomeres only in human chromosomes; 5 ref. to centromeres only in human chromosomes; 6 ref. to operons only in bacteria; (d) (i) 1 much longer DNA molecule; 2 DNA packaging in nucleosomes with DNA wrapped around histones 3 more non-coding DNA in human chromosomes; (ii) 1 multiple sites of replication (on each chromosome);

2007 ‘A’ Level H2 Biology Mark Scheme (updated 10 Jan 2015) 4 QUESTION 4 (a) 1 (inherited) change in DNA/nucleotide sequence/base sequence; 2 base substitution; 3 change in codon/triplet for amino acid/change in R group; 4 base addition/deletion; 5 ref. to frameshift or described; (b) 1 (if addition/deletion resulting in) frameshift; 2 protein coded for no longer synthesized/non-functional; 3 (if substitution resulting in) amino acid changed; 4 change 3D/tertiary structure of protein/different R group; 5 ref. change in binding site ref. to active site is neutral (c) 1 both copies of a tumor suppressor gene must be mutated (before a person will develop cancer); 2 ref. to effect of mutation being masked/ref. to normal allele being dominant/remaining functional copy of gene; 3 sufficient quantities of proteins synthesized to be effective; (d) 1 specific shape of binding site of p53 protein; 2 corresponds to/complimentary to shape, part of DNA molecule; 3 different sequences of bases have different shapes; 4 ref. to major and minor grooves on DNA; (e) 1 change in amino acid in region away from binding area; 2 may not affect shape or binding properties; 3 ref. idea some amino acids coded for by more than 1 codon/triplet of bases/ref. genetic code/some codons degenerate; 4 change in base/codon may not change amino acid/neutral;

2007 ‘A’ Level H2 Biology Mark Scheme (updated 10 Jan 2015) 5 QUESTION 5 (a) RRPP RRPp RrPP RrPp (b) parents RRpp x rrPP; gametes Rp x rp F1 RrPp; RrPp x RrPp gametes RP, Rp, rP, rp RP, Rp, rP, rp; F2 walnut rose pea single ;; R R P P R R p r r P P r r p p R R P p x 2 R r p p r r P p R r P p x 4 R r p p r r P p R r p p x 2 (allow on Punnett square, all genotypes must be shown, correspond to correct phenotype) (c) RrPP x RRpp RRPP x Rrpp RRPP x RRpp

2007 ‘A’ Level H2 Biology Mark Scheme (updated 10 Jan 2015) 6 QUESTION 6 (a) P nucleus / euchromatin / nucleoplasm / chromatin; R: heterochromatin Q nuclear envelope; R cell surface membrane; (b) 1 site of cellular respiration / oxidative phosphorylation / aerobic respiration; 2 synthesis / production / release of ATP; 3 ref. specific use of ATP (e.g. active transport / vesicle transport / mitosis / macromolecule synthesis, incuding DNA replication, transcription and translation); 4 ref. ATP produced by mitochondria released into cytosol while ATP in chloroplasts not; (c) (i) 1 double membrane; 2 highly folded / large surface area of inner membrane; 3 presence of ETC / proton pumps; 4 ATP synthase; 5 70S ribosomes; 6 DNA loops; (ii) 1 three membranes / double outer membrane in chloroplasts; 2 ref. position of stalked particles / chloroplasts “inside out” 3 starch grains; 4 stack of thylakoid membranes / grana; 5 ref. to thylakoids once; 6 no cristae in chloroplasts; 7 contain pigments / chlorophyll; A: other photosynthetic pigments (d) 1 oxidative phosphorylation: final e- (and H+) acceptor / combines with e- and H+ to form water; 2 photophosphorylation: (waste) produce / from photolysis

2007 ‘A’ Level H2 Biology Mark Scheme (updated 10 Jan 2015) 7 QUESTION 7 (a) (dot correct answers then ticks bottom right of page) a n i m a l ; p h y l u m ; c l a s s ; o r d e r ; D i c r u r u s ; s p e c i e s ; 6 c o r r e c t = 4 5 c o r r e c t = 3 4 correct = 2 3 correct = 1 (b) 1 ref. inherited variation/variation in alleles; 2 ref. natural selection; 3 differences in selection pressures in different habitats; 4 ref. to survive to pass on alleles; 5 geographical isolation / ref. allopatric; 6 idea that broadleaved woodland not continuous; 7 ref. islands; 8 prevents interbreeding / gene flow; 9 ref. to genetic drift/founder effect; (c) 10 similar (morphological/anatomical/physiological) features; 11 capable of interbreeding; 12 to produce fertile offspring;

2007 ‘A’ Level H2 Biology Mark Scheme (updated 10 Jan 2015) 8 QUESTION 8 (a) Cellulose 1 a polysaccharide; 2 (chain of) β/beta glucose; 3 1-4 links; (glycosidic bonds not as important as linking bonds) 4 ref. to microfibrils; 5 ref. to bundles of microfibrils/macrofibrils/fibres; Collagen 1 a fibrous protein; 2 (chain of) amino acids; 3 ref. to peptide bonds; 4 ref. to each chain helical; 5 triple helix/tropocollagen; 6 ref. to role/presence of glycine; 7 ref. to staggered ends; 8 ref. to H bonds; A once in either (b) Glycogen 1 a polysaccharide; 2 (chain of) α/alpha glucose; 3 1-4 with (some) 1-6 links/branches; 4 insoluble; 5 (energy) store; 6 stored/produced in muscle/liver; Glucagon 1 a globular protein; 2 (chain of) amino acids; 3 ref. to peptide bonds; 4 soluble in plasma; 5 produced by α/alpha cells in pancreas/islets of Langerhans; 6 a hormone/regulates/raises blood glucose; (c) 1 ref. energy reserves; 2 ref. lipid