DHS 2023 Y5 H2 Promo Answer Scheme (Paper 1 and 2)

1 DUNMAN HIGH SCHOOL Promotional Examination Year 5 H2 Biology Promo Exam 2023 Mark Scheme Paper 1: Multiple Choice Question 1 A 6 B 11 A 2 D 7 D 12 A 3 D 8 B 13 C 4 C 9 A 14 D 5 B 10 B 15 D Q Explanation 1 Region P refers to the nucleoid region and region Q the nucleolus. Statement 1: True Statement 2: RNA synthesise in P and rRNA in Q. Statement 3: ATP synthesis occurs in mitochondria and chloroplasts. Statement 4: Circular DNA found in bacteria, mitochondria, and chloroplasts. 2 The larger the organelle, the lower the centrifugal speed required for the organelle to sediment. Diagram shows the size of the organelles. Liquid 1 contain all organelles except largest organelle – nucleus Liquid 2 –nucleus and mitochondria removed Liquid 3 –nucleus, mitochondria, and endoplasmic reticulum removed 3 Statement 1 is false: Triglycerides have hydrophobic regions too. Statement 2 is false: The fatty acids in a triglycerides may not be always saturated. Statement 3 true. Statement 4 is false: Phospholipids is polar whereas triglycerides is non-polar. 4 Statement 1: glucose monomers arranged in the same orientation will give a helical structure thus structure is compact and thus suitable as energy store. Statement 2: Fact. But does not account for starch being suitable as an energy storage molecule. Statement 3: amylopectin is more branched than amylose. So more compact and thus a suitable as energy store. Statement 4: will remain insoluble at room temperature so suitable as energy store. Statement 5: Fact. But does not account for starch being suitable as an energy storage molecule.

2 5 Graph is an endothermic reaction activation energy graph. Statement 1: X shows potential energy of reactants. Statement 2: Y shows activation energy. Statement 3: you need to see another graph showing lowering of activation energy to be sure that enzyme is added to the reaction. Statement 4: This is factual statement but cannot be concluded from the graph since there is no information about proximity effect. Statement 5: can see from graph. . 6 X has ribose sugar and Y has deoxyribose sugar. Statement 1: True, X forms 2 hydrogen bonds with T. Statement 2: X has ribose sugar, not deoxyribose sugar. Statement 3: True, Y forms 2 hydrogen bonds with U. Statement 4: No uracil used in replication. 7 Types and amount of DNA in: Picture 1: all double stranded 15N15N Picture 2: all double stranded 15N14N, Picture 3: 50% double stranded 15N14N and 50% double stranded 14N14N. So, it is 25% of DNA is 15N and 75% of DNA is 14N. 8 Statement 1: Fact but not answering question. Statement 2: True, need to have the genome sequence to synthesize primers. Statement 3: Factors e.g. length of genome, type of DNA polymerase used, may determined the temperature used for the three stages. Statement 4: Only sterile technique can ensure that there is no contamination. 9 All bands in the son should be either accounted for by the mother or the father. The bands chosen should undeniably come from the husband aka band 1 and 4. Band 1 inherited from husband. Band 2 can be inherited from wife or male. Band 3 cannot be determined if is inherited from husband or male. Band 4 inherited from husband. Band 5 inherited from either husband or wife. Band 6 can be inherited from husband or wife or male. Band 7 can be inherited from wife or male. Band 8 inherited from wife. 10 DNA fragment 3’ ACCGTCAAT 5’ mRNA codon 5’ CGGCAGCCA 3’ amino acid N-Terminus arg glut pro C-Terminus 11 X: Lysis process in the cycle indicates that it is a lytic cycle. Y: Excision of prophage indicates that it is a lysogenic cycle. A: The bigger one is bacterial DNA. B: Phage genome in bacterial chromosome is called prophage. 12 Since CFU is increasing, this shows that lactose is being used so the entire Lac operon is being transcribed. 13 Statement 1: Unwinding of DNA likely results in upregulation of transcription. Statement 2: May be true but not shown in diagram. Also, it is usually acetylation or deacetylation of histone protein. Statement 3: True. Statement 4: Binding of TAP and TBP to their binding sites is dependent on complementary shape between TAP and TBP and their DNA binding sites.

3 14 16 chromosomes in diagram. Sister chromatids are separated into 2 daughter cells. 15 Centrioles exist as a pair. It is more accurate to call the structure a pair of centrioles. The diagram shows 2 pairs of centrioles . The duplicated centrioles are separated to the opposite poles. During anaphase, centriole to centromere microtubules become shorter so that the sister chromatids are pulled apart. Centriole to centriole microtubules will become longer instead of shorter

4 Paper 2 Section A: Structured Questions Question 1 (a) 1. a stack of smooth surfaced flattened membranous sacs / no ribosomes; 2. not connected to / continuous with (outer membrane of) nuclear envelope; 3. swellings at end of sacs (for vesicle formation) / vesicles at ends of sacs; Accept reverse argument Max 2 [2] (b) Magnification = ______XY_____ Actual diameter Actual diameter = ______XY_____ = 1.35 cm = 0.0000287 cm = 287 nm Magnification 47000 ; Correct calculation; A 276/7 nm (for 13) A 287 nm (for 13.5 mm) A 297/8 nm (for 14 mm) [2] (c) (i) accept points from a diagram 1 phospholipid bilayer; 2 membrane protein; plus any two from: 3 hydrophobic core / fatty acid tails orientated inwards; 4 phospholipids move laterally; 5 integral and peripheral proteins / AW proteins scattered (in phospholipid bilayer) proteins / phospholipids, can move around (in phospholipid bilayer) 6 correct ref. to, hydrophobic / hydrophilic, regions  / AW, on, phospholipid / protein; [3] (ii) any two from: ref. reduced gaps between membrane molecules; higher proportion of phospholipids with saturated fatty acids (means closer packing); fewer unsaturated fatty acids so, fewer 'kinks' in tails / closer packing; ref. lower number of channel / carrier / transport proteins; smaller diameter of channels in non-specific channel proteins; fewer types of (specific), transport/ carrier, proteins; AVP; [2]

5 Question 2 (a) (i) Correct polypeptide product + water molecule formed; (R: R used instead of H for glycine) Peptide bond: correct identification + labelling; Condensation process; (Reject translation since ribosomes and mRNA are not shown). [3] (ii) Peptidyl transferase; (R: ribosome) [1] (b) any three from: accept answers in the context of lactase: 1 ref. to controlled variables; e.g. constant pH / temperature 2 take samples at timed intervals; Accept regular intervals 3 determine, substrate / lactose, concentration   or determine, product / glucose / galactose concentration; 4 plot graph of, substrate concentration / product concentration, against time; 5 ref. to rate of disappearance of substrate or ref. to rate of appearance of product; [3] (c) One of the amino acid/G is changed to a much larger amino acid residue which disrupts the close/compact packing of triple helix / three polypeptides ; (R: no collagen molecule/tropocollagen formed). Less/no covalent cross-links between adjacent collagen molecules, reducing formation of collagen fibrils , and disrupting structure of collagen fibre formed from staggered arrangement of collagen fibrils; [2] (d) As pH increases from pH 5 to pH 7 to pH 10, the swelling ratio of collagen increases from around 150% to 400% to 850% by end of 8 hours; Excess OH - ions at high pH neutralise the positively charged R group of amino acids, breaking the ionic bonds and hydrogen bonds, creating larger / more gaps between collagen molecules, resulting in higher swe