Control of Pathogens (p. 121); Ex 2-13 the Lethal Effect of Ultraviolet Radiatio
ID: 165938 • Letter: C
Question
Control of Pathogens (p. 121); Ex 2-13 the Lethal Effect of Ultraviolet Radiation on Microbial (growth (p. 129-130); Also, read page 727. first paragraph and hg 10-18 the student will be able to: Explain how ultraviolet light affects bacteria and inhibits bacterial growth. Desert be how the antibacterial effect of ultraviolet light can be tested in the lab. Cite limitations and safety considerations associated with using ultraviolet light to control microbial growth. Explain reasons why a bacterium might be relatively resistant to the antimicrobial effect of ultraviolet light. Working as table-teams. inoculate plates for confluent growth with the following organisms and expose to ultraviolet light for various times: Bacillus megaterium Escherichia coli Using your own words, state the two-fold purpose of this experiment. What is the mechanism by which ultraviolet light kills bacteria? After incubation, use a 0 to +3 scale to assess bacterial growth on the unexposed (control) plate and on the covered and uncovered portions of your exposed plates. Constrict a well-organized table showing the results of the experiment of your table-team. Were any bacteria killed on the covered section of the plate? Why or why not? How long did F.. coli persists when exposed to uV light? How long did B. megaterium persist when exposed to uV light? Was there a difference in survival for these 2-bacterial species? How do you explain your results? What safety precautions should be employed when using ultraviolet light to control microbes? (Be specific.) Why?Explanation / Answer
1. The two fold purpose of this experiment is to know the effect of Ultraviolet light on the bacterial cells.
2. Ultraviolet lights kills cells by simply damaging the DNA. If once the bacterial cell is exposed to UV light, it causes mutation I.e, the light initiates a reaction between the two molecules of nucleotide " thymine" bases. Hence results in the formation of a very stable thymine dimer. This can be repaired by excising or removing the two thymine bases and filling the gap with new nucleotides. The longer the cell is exposed to UV light, the greater will be the thymine dimer formation and more will be the damage to the cell. Hence damages the cells and the organisms (bacteria).
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