2019 EJC Promo JC1 P2 Bio (Q)

©EJC 2019 9744/02/J1H2PromotionalExamination/2019 [Turn over EUNOIA JUNIOR COLLEGE JC1 Promotional Examinations 2019 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CIVICS GROUP 1 9 - REGISTRATION NUMBER H2 Biology Paper 2 Structured Questions & Free Response Questions 9744/02 04 October 2019 2 hours Candidates are to answer all questions in section A in this question booklet. READ THESE INSTRUCTIONS FIRST Write your name, civics group and registration number on all the work you hand in. There are two sections in Paper 2, sections A and B. Answer all questions. Write in dark blue or black pen on both sides of the paper. You may use an HB pencil for any diagrams or graphs. Do not use paper clips, highlighters, glue or correction fluid. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 17 printed pages and 1 blank page. For Examiner’s Use Section A 1 2 3 4 Section B 5 Total 80

2 ©EJC 2019 9744/02/J1H2PromotionalExaminations/2019 For Examiner’s Use BLANK PAGE

3 ©EJC 2019 9744/02/J1H2PromotionalExaminations/2019 [Turn over] For Examiner’s Use Section A Answer all the questions in this section. 1 Fig.1.1 is an electron micrograph of an animal cell. Fig 1.1 (a) (i) Identify the organelles A and B shown in Fig 1.1. [2] A: nucleus B: mitochondrion Examiner’s comments: If the arrow is pointing at one organelle, use the singular term. For example, mitochondrion instead of mitochondria (plural). (ii) Compare the structures of both organelles. [3] Similarities: 1. Both nucleus and mitochondrion are enclosed by a double membrane 2. Both contain DNA; Differences: 3. Mitochondrion has a highly folded inner membrane forming cristae, while the inner nuclear membrane is not folded; 4. Nucleus has nuclear pores in its nuclear envelope, while mitochondrion does not have pores in its double membrane; 5. AVP Examiner’s comments: For comparison questions such as this, please compare point-to-point and do not write in chunks. Note that the nucleus is also bounded by a double membrane (nuclear envelope). If size is stated as a point of comparison, give an approximate range else the point of comparison (bigger vs. smaller) looks weak. B A

4 ©EJC 2019 9744/02/J1H2PromotionalExaminations/2019 For Examiner’s Use The nucleus does not contain 80s ribosomes. Only ribosomal subunits are synthesized in the nucleolus. Assembly of 80s ribosomes occurs in the cytoplasm. Other accepted answers included: - DNA in nucleus is linear v.s. DNA in mitochondrion is circular. Protons are transported across the inner mitochondrial membrane through a transport protein depicted in Fig 1.2. This transport protein also serves as an enzyme that drives the synthesis of ATP from ADP and an inorganic phosphate ion (Pi). Fig 1.2 (b) Using Fig. 1.2, (i) identify the type of transport protein. [1] 1. Channel protein R: carrier protein / pump (ii) state and describe the process by which protons are transported across the inner mitochondrial membrane. [3] 1. Facilitated diffusion; R: diffusion / osmosis / active transport 2. Protons move through the hydrophilic pore of the channel protein; 3. down their concentration gradient from intermembrane space to mitochondrial matrix; R: using energy / ATP hydrolysis Examiner’s comments: Several students did not indicate the process of movement of protons – facilitated diffusion. Incorrect answers included active transport and passive diffusion. Protons are charged (not polar!) hence they are unable to move across the hydrophobic core of the phospholipid bilayer. Direction of movement from intermembrane space to matrix must also be stated. [Total: 9] H H H H H H H H H H H H H ADP + AT

5 ©EJC 2019 9744/02/J1H2PromotionalExaminations/2019 [Turn over] For Examiner’s Use 2 Fig 2.1 shows an error occurring during the second meiotic division of primary spermatocytes of an unknown animal. Fig. 2.1 (a) (i) Complete Fig 2.1 to show the correct structures and number of chromosomes within the gametes. [1] n+1 and n-1 in the first two gametes, normal haploid (n) third gamete R: metaphase chromosome (X-shaped), or if all gametes are haploid (n) Examiner’s comments: • Many students drew a metaphase chromosome in either of the first two gametes, which is incorrect. Although there was a failure of centromere division during anaphase II, by the time telophase and cytokinesis have occurred, the proteins holding the centromeres together would have dissociated, and the two chromatids would separate into chromosomes in the same gamete. (ii) Describe and explain how the error depicted in Fig 2.1 may have occurred. [3] 1. Arising from a non-disjunction event; 2. due to failure of separation of sister chromatids during anaphase II; 3. Caused by centromeres failing to divide OR improper / unequal shortening of kinetochore microtubules / spindle fibres; Examiner’s comments: • This question was generally well done, with most students able to explain how aneuploidy arises. However, many students did not identify the error as a non- disjunction event, and focussed instead on the consequences (aneuploidy), which was not asked for. Meiosis Primary spermatocytes (2n) Meiosis Gamete Secondary spermatocytes (n)

6 ©EJC 2019 9744/02/J1H2PromotionalExaminations/2019 For Examiner’s Use Testis cells undergo several rounds of mitosis to differentiate into primary spermatocytes. Fig 2.2 shows the different phases of the cell cycle. Arrows indicate checkpoints of the cell cycle, and brief descriptions of the G1 and G2 checkpoint criteria are given. The M checkpoint occurs during metaphase of mitosis. Fig. 2.2 (b) (i) State the criteria for the cell to pass the M checkpoint. [1] 1. Check for proper attachment of spindle fibres / kinetochore microtubules to the centromere of each chromosome; Examiner’s comments: • Many students stated the alignment of chromosomes along the metaphase plate, which though important, is not the key criteria of the M checkpoint. • Some students also incorrectly stated that proper separation of homologous chromosomes to opposite poles of the cell, which only occurs during anaphase (after the M checkpoint). (ii) With reference to Fig 2.2, describe how the dysregulation of cell cycle checkpoints could lead to cancer. [3] 1. Dysregulation of cell cycle checkpoints means that cells will continue to divide despite failing to meet the criteria to satisfy each checkpoint; 2. For instance, mitosis proceeds even in absence of growth factors / presence of damaged DNA [quote at least one criterion from Fig 2.2]; 3. Thus, uncontrolled cell division and accumulation of further genetic mutations over multiple rounds of DNA replication occurs could result in cancer. Examiner’s comments: • The first point on explaining what dysregulation of cell cycle checkpoints entails was poorly answered by most students. • A common erroneous answer was to explain how dysregulation of each checkpoint could result in a different consequence that might lead to cancer. • For this question, all three checkpoints simply s erve to regulate the cell cycle, and a dysregulation of these checkpoints (due to spontaneous mutation or