3. In part 4 B, you plated cells after heating in a 160∘C oven for two minutes, after placing the tube in boiling water

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3 In Part 4 B You Plated Cells After Heating In A 160 C Oven For Two Minutes After Placing The Tube In Boiling Water 1 (43.16 KiB) Viewed 44 times

3 In Part 4 B You Plated Cells After Heating In A 160 C Oven For Two Minutes After Placing The Tube In Boiling Water 2 (37.69 KiB) Viewed 44 times

3. In part 4 B, you plated cells after heating in a 160∘C oven for two minutes, after placing the tube in boiling water (100∘C), and after placing a tube in 63∘C water. We often see that more cells survive the dry heat exposure (160∘C ) better than the other two treatments (which are at lower temperatures). Propose an explanation for this observation. 4. If 90% of the bacteria in a culture are killed in 20 seconds, then how many would be killed in 40 seconds? In 60 seconds? How long would it take for "sterilization" to occur? 5. UV is a mutagen - it damages the DNA. We wrapped the plates with Aluminum foil to prevent these mutations from being repaired by a light-activated DNA repair enzyme found in bacteria. Describe a modification to the experimental desiga that would allow you to determine whether bactericidal activity of the UV lamp was reduced by the presetice of visible light. 6. In this lab, we tested the ability of UV to kill Serratia marcescens, a pigmented bacteria. E. colt, which is closely related to S. marcescens, is unpigmented. Do you think E. coll would less, more, or equally sensitive to UV, compared to S. marcescens? Explain your answer.
8. We found that UV was effective at killing bacteria. Why is it not used more often? What disadvantage of UV as a germicidal treatment was evident? 9. What other kinds of irradiation are used to sterilize things like plastic lab materials and foods? 10. Backpackers camping in the wilderness sometimes need to treat their own drinking water, which they obtain from a lake or stream. One popular method of water treatment is filtration. Camping supply stores sell inexpensive filtering systems, which typically have pore sizes larger than 0.45 micrometers. From the perspective of microbiology, are there any concems with this practice? 11. Portable UV sources are available for travelers to treat water. Water from some sources is "turbid" due to the presence of suspended particles. Will this affect the ability of a UV water purifier to make the water safe?