SAJC 2023 H2 BIO P2 ANS

Civics Group Index Number Name (use BLOCK LETTERS) ST. ANDREW’S JUNIOR COLLEGE 2023 JC2 PRELIMINARY EXAMINATIONS H2 BIOLOGY 9744/2 Paper 2 Monday 28 th August 2023 2 hours Materials: Question Paper READ THESE INSTRUCTIONS FIRST Write your name, civics group and index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagram, graph or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions. Write your answers in the spaces provided on the question paper. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiners’ Use 1 /13 2 /10 3 /12 4 /12 5 /14 6 /9 7 /11 8 /9 9 /5 10 /5 Total /100 This document consists of xx printed pages and x blank page. [Turn over H2

QUESTION 1 Fig. 1.1 is an electron micrograph that shows part of a eukaryotic cell. Fig. 1.1

(a) Organelle B is made of two types of molecules. (i) Name the molecules in organelle B and state the process and location where each molecule is synthesized, by completing the table below: Organelle B Molecule 1 Molecule 2 1 Name ribosomal {RNA / ribonucleic acid(s)} protein(s) 2 Process transcription translation 3 Location nucleolus cytoplasm (ii) Identify the organelle B in Fig. 1.1 and state one function of this organelle. …………………………………………..……………………………………………………………[2] 1 Ribosome; Function : any one 2 Sites of {translation of mRNA into polypeptides / synthesis of protein} ; 3 Ribosomes contain binding sites for both tRNA and mRNA ; 4 Peptidyl transferase activity present in the large ribosomal subunit catalyse the formation of peptide bonds between amino acid; (b) Collagen is a protein produced by cells and is the most common structural protein, due to its high tensile strength, in vertebrates. (i) To form collagen, many of the amino acids such as proline and lysine are modified by the addition of a hydroxyl group on its side chain to form hydroxyproline and hydroxylysine residues, respectively. Vitamin C is necessary in aiding this conversion of proline and lysine to hydroxyproline and hydroxylysine. Vitamin C works by preventing the inactivation of two key enzymes, lysyl and prolyl hydroxylas, in collagen biosynthesis. Fig. 1.2 shows the synthesis of collagen. Production of tropocollagen starts with procollagen Procollagen, once secreted outside the cell, will be cleaved at C and N terminus to form tropocollagen.

Fig. 1.2 Describe how the procollagen is synthesized and secreted out of the cell to be assembled into collagen. ………………………………………………………………………………………………[6] (Procollagen is made up of 3 polypeptide chains) 1 Each polypeptide is first synthesized by the ribosomes on the rER; [Reject: polypeptide folds into its native / 3-dimensional conformation (only applies to globular proteins)] ; 2 Ref. entry of polypeptide into RER lumen; where specific amino acids in polypeptide chain undergo chemical modification with hydroxyl groups are added to proline and lysine to form hydroxyproline and hydroxylysine ; 3 The modified proteins are packaged into transport vesicles which buds off the RER and move towards of Golgi body at the cis face; 4 Further chemical modification of the protein occurs in the Golgi body (e.g. proteolysis, glycosylation, phosphorylation etc.); 5 [Based on context] Ref: presence of key enzymes, lysyl and prolyl hydroxylase, in lumen of RER or Golgi body ; (which were kept activated by Vit C) 6 Modified proteins (procollagen) are packaged into secretory vesicles which bud off the trans face of the Golgi body; 7 Secretory vesicles move toward the cell surface membrane. The vesicle’s membrane fuses with the cell surface membrane, releasing the modified protein (procollagen) via exocytosis; 8 Movement of transport and secretory vesicles is guided by filaments and microtubules (components of the cell cytoskeleton) with the use of ATP as energy source; 9 Ref. formation of hydrogen bonds {involving OH groups of hydroxylproline (within tropocollagen) / between NH of glycine and CO of other amino acids on the other 2 chains} to stabilize procollagen structure; 10 Ref. formation of covalent bonds involving hydroxylysine (and lysine) between tropocollagen molecules to form fibril s (and association of collagen fibrils to form fiber); [Max 6] (ii) Cellulose is present in plants and functions as a suitable cell wall material. Cellulose is made up of cellulose microfibrils which are formed from cellulose molecule. Each cellulose molecule is a polymer of glucose.

Describe the structure of cellulose molecule. ………………………………………………………………………………………………[2] 1. β-glucose joined by β(1,4) glycosidic bond; 2. Adjacent monomers rotated through 180°; 3. Straight / linear chain; [Total: 13]

QUESTION 2 Chemotherapy is used in the treatment of cancers. Common side effects during chemotherapy treatment include fatigue, hair loss, infection, etc. While the survival rate has increased due to chemotherapy for some cancers, e.g breast cancer, the quality of life has decreased because of the side effects of chemotherapy. For some patients, fatigue may persist for months or even years after the end of cancer treatment, thus affecting the physical functioning and mental health of these patients. Various toxins are being developed as alternatives to cancer treatments, and bee venom is drawing attention as one of them. Several studies have demonstrated one of the components in bee venom, melittin, has anti-cancer effects. Melittin is a polypeptide composed of 26 amino acids. It is an amphoteric molecule owing to the specific arrangement of amino acids, with nonpolar, hydrophobic and neutral amino acids at the end of the N-terminus, and hydrophilic and basic amino acids near the C-terminus. Research has showed that melittin incorporates into and disrupt the functions of natural and synthetic membranes by forming pores for ions, which eventually leads to disorder in the structure of phospholipid bilayers. (a) Explain how the molecular structure of the phospholipid allows for the formation of the phospholipid bilayer. ………………………………………………………………………………………………………[2] 1 Phospholipid molecule consists of (one) h ydrophilic / polar phosphate head (of phospholipid) ; (two) hydrophobic / non-polar fatty acid tails; 2 Ref. ionic bonds or hydrogen bonds between phosphate heads or between phosphate heads and aqueous medium of the cytoplasm and the external environment / hy drophobic interactions between fatty acid tails; (facing away from the aqueous medium) (b) Explain why ions can only cross the membrane via the pores formed by melittin. ……………………………………………………………………………………………………...[3] 1 Ions are charged [state chemical property] (thus ions are hydrophilic [state physical property ie water loving or water hating] ) 2 (Ions are) therefore unable to pass through the hydrophobic core of the cell membrane ; 3 [state what melittin protein can provide ie the reason for necessity of protein] The transport of ions require specific proteins such as melittin to provide a water-filled / hydrophilic channel; (c) Suggest a possible disadvantage in using melittin as an anti-cancer drug. ………………………………………………………………………………………………………… ………………………………………………………………………………………………,,,,,,,…[1] 1 Melittin does not distinguish normal or cancer cell membranes / will damage phospholipid bilayer structures in both normal and cancer cell ;

(d) Explain, using honey bee as an example, how an aspect of the natural environment may affect phenotype. ………………………………………………………………………………………………………[4] Reproductive system in Honey Bees 1 Although both queen and workers are females developed from fertilised dipl