SAJC_2009_H2-Bio-TYS-ANS

2009 UCLES ‘A’ Level H2 Biology Mark Scheme 1 2009 ‘A’ Level H2 Biology Mark Scheme PAPER 1 (MCQ) 1 A 21 B 2 C 22 C 3 A 23 D 4 D 24 A 5 D 25 C 6 A 26 B 7 B 27 B 8 D 28 B 9 B 29 B 10 D 30 C 11 C 31 B 12 D 32 B 13 D 33 C 14 D 34 A 15 C 35 B 16 B 36 B 17 B 37 B 18 C 38 C 19 C 39 B 20 A 40 C

2009 UCLES ‘A’ Level H2 Biology Mark Scheme 2 PAPER 2 (CORE) QUESTION 1 (a) A – mRNA B – polypeptide C – cisterna/lumen of rough endoplasmic reticulum (reject RER/cristae) (b) Location Ribosome present Ribosome absent Nucleus √ Chloroplast √ Vacuole √ Mitochondria √ 4 c o r r e c t = 2 3 c o r r e c t = 1 (c) 1 allows the movement of synthesized polypeptide across the membrane; 2 functions as a receptor to bind the signal recognition particle/signal peptide of the polypeptide; 3 functions to hold the ribosome so that the polypeptide can be inserted into the ER lumen. (d) 1 transport vesicle carrying the protein buds off the rough endoplasmic reticulum and transported to and fuse at the cis face of the Golgi body; 2 secretory vesicle buds off the trans face of the Golgi body and transports the protein to the cell surface membrane; 3 Membrane of the vesicle fuses with the plasma membrane and releases the protein via exocytosis; 4 microtubules aid in the transport of the vesicles from the ER to the Golgi body and to the plasma membrane Examiner’s comments: Many candidates unnecessarily wrote about the roles of the RER and Golgi in relation to the proteins. (e) 1 through protein pore/protein channels on cell surface membrane

2009 UCLES ‘A’ Level H2 Biology Mark Scheme 3 QUESTION 2 (a) Bacterial chromosome Plasmid 1 larger, with more genes smaller, with fewer genes 2 has genes coding for production of enzymes for cell metabolism has genes coding for genetic markers such antibiotic resistance Examiner’s comments: Need to mention exactly what the genes are coding for. (b) (i) 1 Sex pilus of the F+ donor cell makes contact with the F- recipient cell 2 Replication and transfer of F plasmid from F+ into F- cell (ii) 1 Foreign DNA taken up by bacteria through its cell wall and plasma membrane 2 and is incorporated into bacterium’s DNA via genetic recombination (homologous recombination or site-specific insertion) (c) 1 Acquire antibiotic resistant genes 2 Acquire genes that confer ability to use a new metabolite 3 Acquire genes for other xenobiotic resistance ( A xenobiotic is a chemical which is found in an organism but which is not normally produced or expected to be present in it) Examiner’s comments: Avoid making vague statements about helping bacteria to survive, increase variation or having same characteristics as donor. (d) 1 phage attaches to specific receptors on bacterial cell wall and injects viral DNA into bacterial cell 2 expression of viral genes produces