a Post-lab discussion for an exercise in BIO 120 Laboratory.

1. Exercises 5: Post-Laboratory Discussion for Sterilization

2. v Set-up B: Set-up A: Set-up C: Set-up D: Non-sterile medium in a Sterile Petri dish Sterile medium in a Sterile Petri dish Non-sterile medium in a Non-sterile Petri dish Sterile medium in a Non-sterile Petri dish

3. Results

4. After 24 hours of incubation

5. Non-sterile medium in a Sterile Petri dish

6. Sterile medium in a Sterile Petri dish

7. Non-sterile medium in a Non-sterile Petri dish

8. Sterile medium in a Non-sterile Petri dish

9. After 48 hours of incubation

10. Non-sterile medium in a Sterile Petri dish

11. Sterile medium in a Sterile Petri dish

12. Non-sterile medium in a Non-sterile Petri dish

13. Sterile medium in a Non-sterile Petri dish

14. Discussion

15. For Non-sterile Media: The microorganisms form mostly at the center of the medium. For Non-sterile Petri dishes: At first, the microorganisms form mostly in between the wall and the dish. Then, they spread at the surface of the medium.

16. Death Rate α [Microorganisms] Thermal Death Time (TDT) -time required to kill a known population of microorganisms in a specific suspension at a particular temperature. ↑ Temperature, ↓ TDT and ↓ Temperature, ↑ TDT

17. Significance of this experiment: In order to have a successful experiment, the medium and the Petri dish must be properly sterilized.

18. Answers to Guide Questions

20. 2. Explain the difference when performing sterilization in a microbiology laboratory in UP Baguio as compared to UP Manila. What necessary adjustments may be done? There is no difference. Why? We are just concern with the system inside a pressure cooker or an autoclave which is not affected by the pressure and temperature of the outside environment. We can still manage to sterilize culture media and materials in an autoclave (121 o C, 15 psi, 15 mins.) without making any adjustments.

21. 3. Account for the differences in the microbial growth (absent or present) in the four set-ups. Set-up Surface Inner Colony (groups) nsM-sP Present Present Present sM-sP Absent Absent Absent nsM-nsP Present Present Absent sM-nsP Present Absent Present

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