Unit 3: Nutrition, Cultivation and Maintenance - Practice Quiz

1 Microorganisms that obtain energy from light are called:

2 Microorganisms that use carbon dioxide as their main carbon source are called:

3 A microorganism that obtains energy by oxidizing chemical substances is a:

4 Microorganisms that require organic compounds as their carbon source are called:

5 Which nutritional type obtains electrons from inorganic compounds?

6 Which technique is commonly used to obtain isolated colonies on an agar plate?

7 The main purpose of serial dilution is to:

8 In the pour plate method, a diluted sample is mixed with:

9 A visible mass of microorganisms growing on solid medium is called a:

10 Which method spreads a measured sample over the surface of solid agar?

11 A pure culture contains:

12 The transfer of one isolated colony to fresh sterile medium is called:

13 Which tool is commonly used to transfer a microbial colony?

14 A culture containing more than one microbial species is called a:

15 Which observation most strongly suggests that a culture is pure?

16 The main purpose of preserving microbial cultures is to:

17 Which method preserves microorganisms by storing them at very low temperatures?

18 Lyophilization is also known as:

19 A common protective substance added before freezing microbial cultures is:

20 A culture maintained for regular laboratory use is often called a:

21 A microorganism obtains energy from sunlight and uses carbon dioxide as its principal carbon source. Which nutritional category best describes it?

22 A bacterium oxidizes inorganic ammonia for energy and obtains carbon from carbon dioxide. Which category does it belong to?

23 A microorganism grows in the dark by oxidizing glucose and using organic compounds for cell carbon. Which classification is most appropriate?

24 A bacterium uses light as its energy source but requires organic acids as its carbon source. Which nutritional type is indicated?

25 A culture grows only when an organic growth factor is added, although it can use ammonium salts and glucose. The organism is most likely a:

26 A mixed bacterial sample is expected to contain both abundant and rare species. Which initial method is most suitable for obtaining well-separated colonies?

27 A sample contains a target organism in very low numbers and several competing species. Which approach would best increase recovery of the target organism?

28 A microbiologist wants to estimate viable bacterial concentration before plating a sample. Which procedure is most appropriate?

29 A water sample contains bacteria that are expected to be present at approximately cells per milliliter. Which dilution is most likely to produce a countable plate when mL is spread?

30 A researcher needs to isolate bacteria that can grow without oxygen. Which cultivation strategy is most suitable?

31 After streaking a mixed culture, several colony types appear. What is the best next step to obtain a pure culture of one colony type?

32 A plate contains colonies that are close together, making colony selection uncertain. Which action would most effectively improve purification?

33 A culture appears uniform on an agar plate but may contain cells with different physiological properties. Which test is most useful for checking purity initially?

34 A mixed culture contains one organism that forms large colonies and another that forms very small colonies. Which purification method could exploit this difference?

35 A culture becomes contaminated during transfer because the loop contacts the bench. Which practice would best prevent this problem in future transfers?

36 A bacterial strain must be stored for several years with minimal genetic and physiological change. Which method is generally most suitable?

37 Why is frequent subculturing generally avoided when maintaining a microbial stock culture?

38 A laboratory freezes bacterial cells at very low temperature but observes poor survival after thawing. Which modification may improve recovery?

39 During lyophilization, microbial cells are frozen and then dried under reduced pressure. What is the main purpose of this process?

40 A preserved culture is needed for routine teaching use, but long-term genetic stability is not the primary concern. Which option is most practical?

41 A microorganism obtains energy by oxidizing reduced inorganic compounds, uses CO2 as its principal carbon source, and fixes carbon through the Calvin cycle. Which nutritional classification best describes it?

42 A bacterium grows only in the presence of light and an organic carbon source, but it cannot use reduced inorganic compounds as electron donors. Which classification is most appropriate?

43 A culture grows in darkness using acetate as both its carbon and electron source, while ATP is generated by oxidation of acetate. Which change would most directly convert its nutritional mode to chemolithoautotrophy?

44 An organism uses light to generate ATP but obtains reducing power and cellular carbon from an organic compound. Which statement correctly distinguishes it from a photoautotroph?

45 A microorganism grows poorly on a defined medium but grows normally when yeast extract is added. Its growth is restored by several unrelated organic compounds rather than by one specific metabolite. What is the best interpretation?

46 A mixed sample contains one organism at approximately cells/mL and another at cells/mL. Which isolation strategy gives the rare organism the greatest practical advantage during initial recovery?

47 A soil organism is suspected to be slow-growing and nutritionally fastidious. Which approach is most likely to recover it without allowing rapidly growing heterotrophs to dominate?

48 A facultative anaerobe is being isolated from a specimen containing obligate aerobes and obligate anaerobes. Which design most effectively selects for the facultative anaerobe while preserving recovery of viable cells?

49 When isolating bacteria from a sample with substantial clumping, why can a standard serial dilution underestimate viable cell concentration?

50 A target bacterium is inhibited by the indicator dye in a commonly used differential medium but grows well on a nonselective medium. Which modification best preserves isolation while retaining phenotypic screening?

51 After streak plating, two colony morphologies appear, but microscopy shows that both contain the same cell type. Which conclusion is most justified?

52 A culture repeatedly yields colonies with identical morphology, but sequencing detects two closely related organisms. Which purification method is most appropriate?

53 A mixed culture contains a target organism that grows more slowly than a contaminant but is resistant to a specific antibiotic. Which sequence most effectively purifies the target?

54 A culture passes three rounds of colony purification, yet occasional colonies differ in antibiotic susceptibility. Which explanation should be investigated first?

55 A researcher selects a single colony from a crowded plate where neighboring colonies touch, then reports a pure culture. What is the principal flaw in this procedure?

56 For long-term preservation of a bacterial strain that loses plasmids during repeated subculture, which strategy best minimizes genetic and physiological drift?

57 Why is a cryoprotectant such as glycerol used when bacterial cells are frozen for preservation?

58 A bacterial stock repeatedly loses viability after freeze-thaw cycles even though the initial freezing protocol was effective. Which corrective action is most appropriate?

59 A strain survives lyophilization but shows a long lag phase after rehydration. Which interpretation is most defensible?

60 A culture stored on agar slants remains viable but gradually changes colony morphology after many transfers. Which preservation principle would best prevent this problem?