ly\' ior i a) growth factor b) wheaties c) pyrimidine/purine complex d) micronut

Question

ly' ior i a) growth factor b) wheaties c) pyrimidine/purine complex d) micronutrient e) macronutrient 17. Which of the following devices or procedures for controlling bacterial populations is most likely to be bacteriostatic rather than bactericidal? a) autoclaving b) ultraviolet lamp radiations c) boiling water d) freezing temperatures e) gamma irradiation 18. The 'phenol coefficient' test shows: a) that phenol is the most suitable antiseptic for general use b) that no bacteria can survive exposure to a 5% phenol solution for 30 minutes c) the comparative bactericidal activity between other compounds and phenol d) the pronounced bacteriostatic activity of weak solutions of phenol e) the pronounced fungistatic activity of phenol 19. It would not be practical to use ultraviolet radiation (UV) to sterilize the culture media that you get for the laboratory exercises because: a) thymine dimers would form in the media components b) proteins in the media would be alkylated and would not support bacterial growth c) the media would need to be exposed too long and would become radioactive d) uv radiation will not penetrate glass or liquids (unless the liquids are spread e) chlorinated amino acids may form in the media which could kill bacteria 20. If one ml if a 25 ml sample is placed in 999 ml of dilution water, how much has the original 25 ml sample been diluted?? b) 1: 100 c) 1:1,000 d) 1:10,000 e) 1; 100,000

Explanation / Answer

Ans. #16. D. Micronutrient. A nutrient required in 10-6 order (micro) is called micronutrients.

#17. D. Freezing temperatures. A bacteriostatic method inhibits bacterial growth. The bacteria resumes growth when the means of bacteriostatic control is removed.

# All other methods kill bacteria, and thus are bactericidal.

#18. C. Phenol coefficient is the relative effectiveness of a compound for killing bacteria when compared to that with phenol.

#19. D. Glass absorbs most of UV radiation as well as has low penetration. So, using UV radiation to sterilize culture media is inefficient.

# Thymine dimer is formed in dsDNA. The culture media contain no DNA.

# UV exposure does not effect protein utilization by bacteria because these proteins would ultimately be degraded into free amino acids by the bacteria to use these amino acids to synthesize new proteins as required.

# UV exposure does not make the media radioactive.

#20. C.

Dilution factor = Vol. of sample taken / Total volume made upto

                                    = 1 mL / (1 mL + 999 mL)

                                    = 1 : 1000   

#21. Obligate aerobes

#22. Obligate anaerobes

#23. Facultative anaerobes

#24. Facultative aerobes

#25. Psychrophiles

#26. Mesophiles

#27. Thermophiles

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