Unit 2: Media preparation, sterilization and disinfection - Practice Quiz

1 What is the main purpose of nutrient media in microbiology?

2 Which ingredient commonly provides nutrients in nutrient agar?

3 What is the function of agar in solid culture media?

4 Which instrument is commonly used to measure the volume of water during media preparation?

5 Why is distilled water used in preparing many culture media?

6 What should be done first when preparing reusable glassware for sterilization?

7 Which device is commonly used to sterilize culture media with moist heat?

8 What is the usual purpose of sterilization?

9 Which type of heat is used by a hot-air oven?

10 Which glassware is commonly used to hold culture media on a solid surface?

11 Why should glassware be sterilized before preparing culture media?

12 What does the pH of a culture medium indicate?

13 Which instrument is used to measure the pH of a nutrient medium?

14 Why is a balance used during media preparation?

15 What is the purpose of dissolving powdered media in water?

16 Which item is commonly used to close a flask containing prepared culture medium?

17 What should be checked before using sterilized glassware?

18 What is contamination in a culture medium?

19 Why are media containers not usually filled completely before autoclaving?

20 What is the best general practice when handling sterile glassware?

21 A nutrient agar medium remains cloudy after all ingredients have been added and the flask has been heated. What should be done before sterilization?

22 Why is the pH of nutrient medium adjusted before autoclaving?

23 A flask contains 500 mL of nutrient medium and is tightly sealed before autoclaving. What is the main problem with this setup?

24 Which autoclave condition is commonly used for sterilizing nutrient media when the load is properly arranged?

25 Why should a large volume of nutrient medium receive a longer sterilization time than a small volume?

26 A heat-sensitive antibiotic must be added to sterile nutrient agar. Which procedure is most appropriate?

27 After autoclaving nutrient agar, when is a heat-sensitive supplement usually added?

28 What is the main purpose of using distilled or deionized water when preparing nutrient medium?

29 A student measures 1.5 g of powdered medium instead of the required 15 g for 1 L. What is the most likely result?

30 Why is the final volume of nutrient medium usually adjusted after dissolving the powdered ingredients?

31 Which practice best reduces the risk of nutrient agar boiling over during autoclaving?

32 Which item is most appropriate for checking whether an autoclave cycle has achieved sterilization conditions?

33 Why should air be removed from an autoclave chamber before the sterilization holding period begins?

34 Several clean glass Petri dishes are to be sterilized before use. Which method is generally suitable for dry glassware?

35 Why are glass pipettes commonly wrapped or placed in protective containers before dry-heat sterilization?

36 A glass flask has visible grease and dried medium on its surface. What should be done before sterilization?

37 After sterilizing glassware, a student places it uncovered on a crowded bench for several hours. What is the main concern?

38 Why should sterilized glassware be allowed to cool before handling or using it for media preparation?

39 A nutrient agar plate has many small colonies even though the medium was autoclaved correctly. Which preparation error is most likely?

40 Why should molten nutrient agar be mixed gently after autoclaving and before pouring plates?

41 A nutrient agar formulation requires 15 g agar per liter, but only 600 mL is needed. After dissolving the components, the final volume should be adjusted to:

42 A dehydrated medium specifies 28 g/L, and 750 mL is required. What mass should be weighed?

43 A medium contains a heat-sensitive antibiotic that must be added after autoclaving. Which sequence best preserves both medium sterility and antibiotic activity?

44 Why should a concentrated nutrient medium be mixed thoroughly before aliquoting into bottles?

45 A medium is prepared at pH 7.2, but its pH becomes 6.5 after autoclaving. The most appropriate interpretation is:

46 A flask is filled to 95% of its capacity before autoclaving. What is the principal risk?

47 Which arrangement best supports reliable autoclave sterilization of bottles containing nutrient medium?

48 A sterilized glass bottle is removed from the autoclave while still tightly capped and rapidly cooled under cold water. The major concern is:

49 Why is cotton or a suitable closure used on a glassware opening during dry-heat sterilization?

50 Glassware is visibly clean but contains a thin protein film. Why can this compromise sterilization?

51 A pipette has a narrow, partially blocked tip and is placed in a dry-heat oven. Which outcome is most likely?

52 Which statement best distinguishes validation from monitoring of a glassware sterilization cycle?

53 An autoclave indicator tape changes color, but a biological indicator from the same overloaded cycle is positive. What is the best conclusion?

54 A sugar-containing medium is autoclaved for substantially longer than validated. Which effect is most plausible?

55 A powder medium forms persistent clumps during preparation. Which corrective action is most appropriate?

56 Why should final volume generally be adjusted after the dehydrated medium has dissolved?

57 A glass measuring cylinder is used to prepare exactly 1 L of culture medium. Which practice gives the most accurate final concentration?

58 After autoclaving, a nutrient agar appears clear at room temperature but later forms crystals. Which explanation is most likely?

59 A sterilized bottle is opened on the bench to cool before pouring plates. Which change would most directly reduce contamination risk?

60 A laboratory sterilizes empty glassware in a dry-heat oven but uses the same temperature and time for densely packed loads and loosely arranged loads. Why is this poor practice?