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’ Lev