2018 VJC H2 Biology Prelims Paper 3 Answers

Victoria Junior College Prelim Paper 3 answers Section A Answer all the questions in this section. 1 (a) Evaluate the effectiveness of vaccines agains t the rise of antibiotic resistant strains of pnemococcal bacteria. [4] [Max 4] • Highly effective/effect ive to a large extent; • Antibiotic is administered when a bacterial infection has already occurred; • Ref. to the idea that bacteria hav e reached a population large enough to cause disease / symptoms; • Ref. to the idea that bacteri a have multiplied many times; • Ref. to the idea that each time the bacteria divide, their DNA is copied and mistakes in this process can create variations within the population; • Antibiotic resistance can be one of the variations; • Presence of antibiotics can act as a selective pressure; • Select for more resistant bacteria; • Resistant bacteria survive and reproduce; • Pass down their antibiotic resistance alleles; • Increase the frequency of the antibiotic resistance alleles within the bacterial population; • Vaccines are administered prior to an infection; • Ref. to the idea that infection c an be brought under control before bacteria has the chance to multiply; • Antibiotics tend to target one spec ific bacterial protein / mechanism; • Vaccines can expose the immune syst em to a huge number of bacterial proteins / antigens; • Promotes the development of a vast r epertoire of antibodies that can fight against the bacterial infection in various ways; • Ref. to action of antibodies: e.g. ops onisation, agglutination, neutralisation • Ref. to idea that chances of bacteri a simultaneously evolving resistance to counter every type of antibody produced is slim; • Vaccines can curb overuse of antibiotics; (b) Describe how a typical T4 bacteriophage can work against an antibiotic- resistant bacterium. [3] • T4 bacteriophage binds to specific rec eptors on antibiotic-resistant bacterium; • The T4 phage penetrates the bacterium cell wall by contracting its contractile sheath of the tail which drives the hollow tube of the tail into the host bacterium; facilitating the entry of viral DNA; • The phage then replicates its genome and uses the bacterium’s protein synthesis machinery to synthesise phage proteins and structural components; • The T4 phage components assemble around the viral genome to form new mature phage particles;

Victoria Junior College Prelim Paper 3 answers • A phage-coded lysozyme breaks down the peptidoglycan cell wall of the host cell, causing cell lysis and release of the new T4 bacteriophages; • Resulting in the deat h of the bacterium; (c) (i) Using the information given, describe how a bacterium appears to have acquired antibiotic resistance due to the release of such plasmid DNA. [2] • Competent bacteria cells within the population will take up the plasmid DNA via transformation;; • Plasmid DNA may contain genes for antibiotic resistance;; (ii) Suggest how this could lead to