2016 RVHS H2 Biology Prelims Paper 2 Answers

River Valley High School Pg 1 of 22 Year 6 H2 Biology 9648 Paper 2 2016 Preliminary Examination I RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION II CANDIDATE NAME CENTRE NUMBER S INDEX NUMBER H2 BIOLOGY 9648/02 Paper 2 Core Paper 15 Sep 2016 2 hours Additional Materials: Answer Paper READ THESE INSTRUCTIONS FIRST Write your index number and name on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Section A Answer all questions in the spaces provided on the question paper. Section B Answer any one question on the answer paper provided. Circle the question attempted on the cover page. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 / 10 2 / 10 3 / 9 4 / 10 5 / 10 6 / 11 7 / 10 8 / 10 Section B 9 or 10* / 20 Total / 100 _____________________________________________________________________ This Question Paper consists of 23 printed pages.

River Valley High School Pg 2 of 22 Year 6 H2 Biology 9648 Paper 2 2016 Preliminary Examination II Section A (80 marks) Answer all the questions in this section. 1 Fig. 1.1 shows photomicrographs of a zebrafish cell undergoing mitotic cell division. Fig. 1.1 (a) Explain the significance of mitosis in the development of zebrafish. [2] 1. Produces genetically identical cells; 2. resulting in genetic stability in a zebrafish; 3. Allows growth; 4. into a multicellular zebrafish; 5. Allows replacement of worn-out / damaged tissues; Reject: asexual reproduction as context given is zebrafish (b) (i) Identify stage A. [1] Telophase;; (ii) With reference to Fig. 1.1, describe two visible features that support the identification in 1(b)(i). [2] 1. Chromosomes de-condense into chromatins;; 2. Chromatin are gathered at opposite poles of the cell;;

River Valley High School Pg 3 of 22 Year 6 H2 Biology 9648 Paper 2 2016 Preliminary Examination II (iii) Explain the significance of stage D in cell division. [2] 1. Cytokinesis; 2. Separation of cytoplasmic materials; 3. and chromosomes; 4. into two daughter cells; (c) Explain why sister chromatids are genetically identical. [3] 1. Sister chromatids are formed by DNA replication (in S phase); 2. which is semi conservative; 3. The two parental strands separate; 4. Each parental strand act as a template; 5. for the synthesis of a daughter strand; 6. via complementary base pairing; [Total: 10] 2 Human Immunodeficiency Virus (HIV) is a retrovirus which infects immune cells expressing CD4 receptor on its cell surface membrane. (a) (i) Explain the term retrovirus. [2] 1. Obligate parasite; 2. with single stranded RNA/RNA genome (positive sense); 3. Contains enzyme reverse transcriptase; 4. which can reverse transcribe RNA to cDNA; 5. which can be integrated into host chromosome; In 2012, the United States Food and Drug Administration (FDA) approved the OraQuick In -Home HIV Test, which is th e first test kit which can be b ought at pharmacies. If an individual had been infected by HIV for at least a month, there is a low probability of a false-negative result, whereby the kit incorrectly reports a negative result. The test kit relies on the presence of antibodies against gp120 in blood. Antibodies are produced by immune cells in response to exposure to foreign particles. Fig 2.1 shows the change s in concentration of HIV RNA and antibodies against gp120 in the blood stream after HIV infection.

River Valley High School Pg 4 of 22 Year 6 H2 Biology 9648 Paper 2 2016 Preliminary Examination II Fig 2.1 Adapted from Hunt, 2016, Virology, Microbiology and Immunology On-line. http://www.microbiologybook.org/lecture/hiv3.htm (b) With reference to Fig 2.1, (i) describe how the concentration of gp120 antibodies in blood changes in relation to the concentration of HIV RNA in the first 3 months after infection; [2] 1. From 0 to 1 .5 month after infection, concentration of HIV RNA increases from 0 to 900 mgml-1 while concentration of gp120 antibodies remains at 0 mgml-1;; 2. From 1 to 3 months after infection, concentration of HIV RNA decreases from 900 mgml-1 to 50 mgml-1while concentration of gp120 antibodies increases from 0 mgml-1 to 410 mgml-1;; (ii) explain how HIV RNA concentration increases in the first month after infection; [1] 1. HIV RNA synthesised using HIV cDNA; 2. as a template; 3. using host cell machinery;

River Valley High School Pg 5 of 22 Year 6 H2 Biology 9648 Paper 2 2016 Preliminary Examination II (iii) explain why presence of gp120 antibodies is used as a basis for the detection of HIV infection. [2] 1. A month a fter infection, gp120 antibodies concentration in blood increases; 2. and remains high throughout dormant period; or 1. HIV RNA concentration is low after 3 months/during dormancy; 2. May not be accurately detected by kit (leading to false negative test results) Enveloped viruses like HIV leave the host cell via budding, but T4 bacteriophages use a different mechanism for release. (c) Explain why release of HIV differs from the release of bacteriophages. [3] 1. Budding from host cell allows HIV to acquire glycoproteins gp120 and gp41;; 2. which are embedded on host cell surface membrane; 3. While T4 bacteriophages exit the host cell via lysis of host cell; 4. If HIV is released via lysis of host cell, it will not be enclosed by viral envelope/lysis does not allow for virus to acquire viral envelope;; [Total: 10] 3 Part I An in-vitro transcription system allows a DNA segment from yeast to be successfully transcribed under the control of a eukaryotic promoter. Transcription of this DNA segment occurs when purified components (RNA polymerase II and general transcription factors) are added. However, this in-vitro transcription system using purified components occurs at low efficiency, as compared to that using nuclear extract. This suggests that an important gene regulatory protein present in the nuclear extract is missing from the purifi ed components. (a) (i) State a possible identity of the missing gene regulatory protein. [1] Activator protein;;

River Valley High School Pg 6 of 22 Year 6 H2 Biology 9648 Paper 2 2016 Preliminary Examination II (ii) Describe how the gene regulatory protein identified in 3(a)(i) could result in higher efficiency of transcription. [1] 1. Binds to enhancer; 2. Increases the probability of (general) transcription factors binding / RNA polymerase (II) binding / forming transcription initiation complex; To search for the DNA sequence to which this gene regulatory protein binds, five segments located upstream of the transcription start site (+1) is each deleted in various experimental set -ups. The TATA box is located 15 ba se-pairs upstream of the transcription start site. Each deleted template is incubated with a non -deleted template, which serves as a control. The four deletion sites are shown in Fig. 3.1. Fig. 3.1 The transcription activity of these deletions in the transcription system using nuclear extract is shown in Table 3.1. Table 3.1 Deletion end point -10 -35 -60 -85 Activity in deleted template / a.u. 0 10 24 23 Activity in non-deleted template / a.u. 23 24 24 23 (b) (i) With reference to Fig. 3.1 and Table 3.1, describe the extent of change in t