EJC 2023 H2 9744 P2 (ans)

©EJC 2023 9744//02/J2H2PRELIM/2023 [Turn over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examinations 2023 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CIVICS GROUP 2 2 - REGISTRATION NUMBER H2 Biology Paper 2 Structured Questions 9744/02 14 September 2023 2 hours READ THESE INSTRUCTIONS FIRST Write your name, civics group and registration number on all the work you hand in. Candidates are to answer: All questions on the Question Paper. Write your answers in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use paper clips, highlighters, glue, or correction fluid/tape. 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 22 printed pages and 2 blank pages. For Examiner’s Use 1 2 3 4 5 6 7 8 9 10 Total

2 ©EJC 2023 9744/02/J2H2PRELIM/2023 BLANK PAGE

3 ©EJC 2023 9744/02/J2H2PRELIM/2023 [Turn over Answer all questions. 1 Fig. 1.1 shows an electron micrograph of a eukaryotic cell. (a) (i) Fill in the table to identify structures A and D and show their functions. Structure Identity Function A Nucleolus (R: nucleus) 1. Site of rRNA synthesis; OR 2. S ite of assembly of ribosomal proteins with rRNA to form small and large subunits of ribosomes / ribosomal subunits; D Cell surface membrane (R: cell membrane) (A: plasma membrane) It acts as a barrier which controls the movement of various substances in and out of the cell due to its partial permeability; @ 1 mark per pair [2] (ii) Using the width of structure C as indicated by the arrow in Fig. 1.1 , calculate the magnification of the electron micrograph. Show your working clearly. 1. Length of arrow = 1.4 cm = 14,000 µm, actual width of chloroplast = 1.4 x 2 = 2.8 µm; 2. Magnification = 14,000 / 2.8 = x5,000 or 5,000 times [2] (R: answers without statement(s) to explain the different components of the equation) Fig. 1.1 B 2 µm D A C

4 ©EJC 2023 9744/02/J2H2PRELIM/2023 (b) Fig. 1.2 is an electron micrograph of three cells of the same species of bacterium, Erwinia carotovora. (i) Name two structures found in animal cells which are not present in the cells shown in Fig. 1.2. [2] Any two of the following: 1. Mitochondrion / mitochondria; (R: chloroplast) 2. Nucleus / nuclear membrane / nuclear envelope; 3. Nucleolus; 4. DNA associated with, histones / protein(s); (A: chromosomes / linear DNA) 5. Smooth / rough endoplasmic reticulum; 6. Golgi body / apparatus; 7. Lysosomes / Golgi vesicles / secretory vesicles ; 8. 80S ribosomes; 9. AVP; e.g. cytoskeleton, (9 + 2) microtubules, microfilaments, proteasome, peroxisome, cilium / cilia, flagellum / flagella; (ii) E. carotovora is a rod-shaped bacterium. Explain why two of the bacterial cells in Fig. 1.2 do not appear rod-shaped. [1] 1. Cells not sectioned in longitudinal section; WTTE (A: cross-section shown / depends on angle of cut / cut in different planes / end view) (iii) Scientists think that the origins of structures B and C of Fig. 1.1 were very different from that of eukaryotic cells. The evidence for this is that they both have features in common with bacterial cells like E. carotovora. Compare the structural features of B and/or C with E. carovotora; [3] Similarities: 1. Circular DNA; 2. Small / similar, size; (A: 0.5–15 μm) 3. 70S ribosomes; Difference: Fig. 1.2

5 ©EJC 2023 9744/02/J2H2PRELIM/2023 [Turn over 4. B (mitochondria) and C (chloroplasts) have smaller number of genes / smaller genome / smaller circular DNA compared to bacteria; 5. Chloroplasts have internal membranes folded into thylakoids, whereas there are no thylakoids in bacteria; [Total: 10] 2 Fig. 2.1 is a representation of a starch molecule. Starch is a polysaccharide made up of amylose and amylopectin. (a) (i) Using arrows, label clearly on Fig. 2.1, amylose and amylopectin . [1] Clearly and correctly labelled with arrows as shown above. All or none. (ii) Explain how one structural feature of amylopectin is related to its function in living organisms. [3] 1. Structure: Amylopectin is a very large molecule composed of many α–glucose monomers 2. Property: Thus it is insoluble in water and does not affect water potential of cells; 3. Role: Good energy storage molecule OR 4. Structure: Amylopectin is made up of α-glucose monomers joined together via α- 1,4-glycosidic bonds giving a helical shape within branches; 5. Property: Thus making it a compact molecule; 6. Role: Good energy storage molecule; OR 7. Structure: Amylopectin has α-1,6-glycosidic bonds at branch-points, making it a highly branched molecule / contains numerous branch points; Fig. 2.1 amylopectin amylose

6 ©EJC 2023 9744/02/J2H2PRELIM/2023 8. Property: Provides many ends for enzyme’s easy access to hydrolyse α -1,4 glycosidic bonds between α-glucose monomers to enable rapid release of α- glucose for respiration to provide ATP / faster hydrolysis / for amylase act on at the same time 9. Role: Good energy storage molecule; (b) Cellulose is another polysaccharide. Fig. 2.2 shows three monomers from a molecule of cellulose. (i) State the name of the monomer that makes up cellulose. [1] β- glucose (ii) Cellulose has high tensile strength which makes it suitable for the cell walls of plants. Explain how cellulose has such a high tensile strength making it suitable for the cell walls of plants. [3] 1. Each cellulose molecule consists of alternate β-glucose monomers rotated 180° with respect to each other , linked by β -1,4 glycosidic bond. This results in a linear / straight cellulose chain; 2. Hydroxyl groups project outwards from each linear cellulose molecule allows extensive hydrogen bonds to form between neighbouring parallel chains, forming microfibrils; 3. Microfibrils bundle together to form macrofibrils, which in turn associate together to form cellulose fibres, giving rise to high tensile strength; R: • reference to few OH groups being able available for hydrogen bonding with water molecules • β-1,4 glycosidic bond not easily hydrolysed (c) Glycogen has a similar structure to amylopectin. Glycogen is stored in the liver, kidney and muscles of mammals. State two ways in which the structure of glycogen differs from the structure of cellulose. [2] Any two 1. C ellulose consists of β-glucose monomers while glycogen consists of α- glucose monomers; Fig. 2.2

7 ©EJC 2023 9744/02/J2H2PRELIM/2023 [Turn over 2. Cellulose is a linear molecule / has no branching while glycogen is a highly branched molecule OR Cellulose is a straight molecule while glycogen is a helical molecule 3. Cellulose contains β-1,4 glycosidic bonds between β -glucose monomers, while glycogen contains α-1,4 glycosidic bonds between α-glucose monomers, and α-1,6 glycosidic bonds at branch points; 4. The alternate / adjacent glucose monomers in cellulose are inverted / rotated 180o with respect to each other while the glucose m