DHS 2023 H2 Prelim P1-3 Mark Scheme

1 DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 Biology Preliminary Exam 2023 Mark Scheme Paper 1: Multiple Choice Question 1 D 11 D 21 A 2 D 12 C 22 C 3 C 13 C 23 B 4 A 14 D 24 D 5 A 15 A 25 B 6 D 16 B 26 C 7 A 17 A 27 D 8 B 18 B 28 D 9 B 19 B 29 B 10 C 20 C 30 A

2 Paper 2: Structured Question Question 1 (a) • Ref to Multiple cell types are found in the human capillary such as red blood cells and endothelial cell [name at least 2 cell types]; • which support the cell theory that living organisms are composed of cells; OR • Ref to the nucleus of white blood cell/endothelial cell contains DNA + presence of mitochondria for synthesis of ATP; • which support the cell theory that cells are the basic unit of life; [2] (b) • [Describe] The radioactivity level increased from 60 to 80 arbitrary unit from 5 to 10 minutes; • [Explain] Ref to ribosomes were synthesising new proteins using the radioactive amino acids which contributed to the initial high level of radioactivity; • [Describe] The radioactivity level decreased from 80 to 5 arbitrary unit from 10 to 40 minutes; • [Explain] Ref to the newly synthesised proteins entered the ER lumen and subsequently moved to Golgi apparatus; [4]

3 (c) • Some radioactive proteins synthesised are not secretory proteins hence synthesized by free ribosomes; • some radioactive proteins are rER enzymes and remained in rER; • Some of the newly synthesised radioactive proteins have not reached Golgi apparatus at 40 minutes; Any 2 [2] (d) (i) • Peptidoglycan cell wall; • Circular DNA; • 70S ribosomes; Any 2 [2] (ii) • Primary lysosomes fuse with phagosomes /vesicles containing bacteria taken in via phagocytosis; • Autophagy in which primary lysosomes fuse with vesicles containing worn-out organelles; • Lysosomes contain hydrolytic enzymes to hydrolyse DNA/ protein/ carbohydrates in bacteria and worn-out organelles; [3] Question 2 (a) • Unique number and sequence of amino acids determines bonds and interactions of R groups; • Segments of polypeptide chain coiled into alpha-helices and folded into beta-pleated sheets + stabilized by hydrogen bonds between C=O and N- H groups of polypeptide backbone / peptide bonds; • Further folding into globular structure, stabilised by bonds between R groups – hydrogen bonds, disul fide bridges, hydrophobic interactions and ionic bonds (any 3); [3] (b) • An enzyme has an active site w ith a 3D conformation that is complementary to the protein / polypeptide / peptide bonds it binds and acts on; • The spatial arrangement / charge of the binding and catalytic residues restricts the type of substrates it can catalyse; • As only certain substrates have chemical groups orientated in a manner that would allow formation of temporary bonds with the contact residues to form ES complex; • (Ref. to ES complex) Substrates must also have chemical grou