2022 HCI JC2 H2 Biology Prelims Paper 3 MS

HWA CHONG INSTITUTION / 2021-2022 H2 BIOLOGY / Preliminary Examination Paper 3 / MS 1 HWA CHONG INSTITUTION (COLLEGE SECTION) 2022 JC2 9744 H2 BIOLOGY PRELIMINARY EXAMINATIONS PAPER 3 MARK SCHEME QUESTION 1 (a) Suggest and explain which hunting method is more efficient. [3] 1 *NE method; Any 2: 2 Ref to increased quantity of prey caught /eaten / AW; 3 Ref to conserving energy by not using additional energy for electrical discharge; 4 AVP ; 5 *TT method; Any 2: 6 Ref combination of both electrical and chemical methods to increase effectiveness in immobilising prey; 7 Ref to electrical discharge causing immediate immobilisation of prey; 8 Ref to more effective since direct injection of toxin/ electrical signal into prey; 9 AVP ; (b) Suggest how a cocktail of proteins instead of a single protein is advantageous for the cone snail. [3] 1 (specificity) Ref. to conotoxins having a specific complementary 3D conformations / complementary to a membrane bound receptor; 2 (variety) Ref to higher chance of binding to a receptor/ increase variety of membrane bound receptors that conotoxins can bind to; 3 (effectiveness) Ref. to, conotoxins targeting different prey / many different types of cells in one prey thus increasing success of capturing killing prey ; 4 Single toxin may lead to development of resistance in fish; 5 AVP ; (c) Describe how insulin is able to trigger a response inside the muscle cell. [4] 1 Binding of insulin to RTK triggers aggregation, and dimerization of RTK ; 2 Ref to autophosphorylation/ cross phosphorylation/ phosphorylation of tyrosine residues; 3 Cytoplasmic relay proteins bind and get activated triggering signal transduction pathways / Activated relay proteins acts on downstream proteins and activates them ; 4 Ref to correct description of one cellular response ; - GLUT4 channels / glucose transporters added to cell membranes increasing glucose uptake into cells - Increased use of glucose in respiration / increased rate of glycolysis - increases conversion glucose to glycogen / glycogenesis - Amino acid absorption/ protein synthesis / lipogenesis;

HWA CHONG INSTITUTION / 2021-2022 H2 BIOLOGY / Preliminary Examination Paper 3 / MS 2 (d) (i) Describe the effect of unmodified ρ-TIA on the escape response of zebrafish. [1] As concentration of ρ-TIA increased from 4x10-9 to 5x10-6M, escape response of zebrafish decreased gradually from 9 to 2 (A: lower limit range as values between 2 to 3); (d) (ii) Explain which deletion in the modified ρ-TIA has the greatest impact on its function. [4] 1 *Group 3 ; 2 Quote effect of ρ-TIA on escape response: ie: Increase of modified ρ -TIA from 5 x10 -9M to 1x10 -6M resulted in a reduction of escape response score of 9 to 8 ; R: comparison between group 3 and other groups 3 (effect on protein) ref. to deletion of amino acid sequence resulting in non-functional ρ-TIA / ρ- TIA no longer complementary to receptors / AW ; 4 (effect on fish) Thus unable to prevent flow of calcium into muscle cells/ does not inhibit muscle cells from functioning ; Note: no marks awarded if wrong group identified, or, no group identified even if MP2 to 4 present (iii) Conotoxins are used to develop potential drugs for humans. These drugs can be test ed on zebrafish that are good model organisms since they share 70 percent of their genes with humans. State why zebrafish is used. [2] any two from: 1 (ethics) similar response in zebrafish and humans/ good representation ; 2 (ethics) ref. to no need for human volunteer, sanctity / respect for human life ; R: vague ref to “ethical issue” with no elaboration on humans 3 Quick reproduction rate; 4 AVP ; (e) With reference to Fig. 1.3, (i) Suggest reasons for the high number of species found at the coral reefs. [2] 1 Ref. to high habitat diversity / complex habitat ; 2 Ref. to niches/ abundant microhabitats ; 3 Ref. to coral reefs providing shelter /camouflage against currents/predators 4 AVP; (ii) describe and explain the predicted effect of global warming on the distribution of cone snails within the Philippines. [4] MP1 / MP2 required for full marks 1 (Fig. 1.3a) Quote poleward movement of cone snail species C. tulipa, C. geographus and C. kinoshitai ; 2 (Fig. 1.3b) Quote temperature range will increase above current temperature 25.5- 31.0oC; A: increase in global temp will beyond 30.8oC 3 (Fig. 1.3c) Cone snail species wit h black shells are disadvantaged as they absorb more heat / ORA ;

HWA CHONG INSTITUTION / 2021-2022 H2 BIOLOGY / Preliminary Examination Paper 3 / MS 3 4 Ref to effect of increasing temp on cone snail (e.g denaturation of enzymes) ; 5 Cone snail species can undergo selection in new environment/ risk extinction ; R: disappearance (vague) 6 Global warming causing coral bleaching leading to loss of habitat; 7 AVP ; (iii) Identify one challenge of using morphology to classify cone snails. [1] 1 Reference to subjectivity/ difficulty in determining differences/ non-quantitative; (f) (i) Suggest why it is useful to include gaps as indicated by dashes in Fig. 1.4 when aligning the nucleotide sequences. [1] 1 Ref to adjusting for insertions / deletions in some sequences ; I: comparisons to be done easily / more clearly (vague) (f) (ii) Explain what conclusions can be drawn from the data in Fig 1.4. [3] Any 3: 1 Ref to example with correct species quoted + correct no. of differences in bases ; 2 Ref to smaller the number of differences being more closely related/ more recently diverged / ORA; 3 all the species share a recent common ancestor ; 4 AVP; (f)(iii) Explain why there is insufficient evidence from Fig 1.4 to draw conclusions about the evolutionary relationships between cone snails. [2] Any 2: 1 the nucleotide sequences are only a small fraction of the whole genome ; 2 use of figures to support ; e.g. 20 nucleotides equivalent to, (only) 6 amino acids 3 cytochrome is likely to be a larger, polypeptide / protein / ref. to length of gene ; 4 there will be variation within each species ; 5 these sequences come from one individual from each species ; 6 AVP ; [Total: 30]

HWA CHONG INSTITUTION / 2021-2022 H2 BIOLOGY / Preliminary Examination Paper 3 / MS 4 QUESTION 2 (a) State and explain the potency of the pituitary stem cell in Fig. 2.1. [2] 1. multipotent ; R: pluripotent / totipotent 2. as it can only differentiate into a limited number of / 6 different cell types / specialized cells / AW ; NB: No credit awarded at all if level of potency is incorrect (b) Explain how one feature of stem cells enables them to be a possible preferred treatment over hGH injections. [2] 1. *stem cells can undergo long-term, self-renewal / proliferation by mitotic divisions; A: long periods of time R: unlimited / indefinite 2. producing a constant pool of stem cells ; 3. *stem cells can differentiate into specialized cells ; 4. producing / expressing hGH ; 5. ref. to hGH from injections being degraded by the body over time / need for daily injections to sustain hGH levels in the body ; NB: *MP1 or MP3 is compulsory for full credits (c)(i) Suggest why mRNA was collected for this study instead of DNA. [1] any 1 1. ref. to presence of mRNA indicates that the gene(s) were expressed / transcribed / AW ; 2. ref. to presence of DNA will not be ab