Unit 4: Microbial Growth and Reproduction - Practice Quiz

1 Which phase of the bacterial growth curve occurs immediately after cells are transferred to a new medium?

2 During which phase do bacteria usually divide at their fastest and most constant rate?

3 What is a major feature of the stationary phase?

4 What does generation time mean?

5 If a bacterial population doubles every 20 minutes, what is its generation time?

6 What is a batch culture?

7 In a continuous culture, fresh medium is continuously added while an equal amount of culture is removed. What is this process called?

8 What is the main characteristic of a synchronous culture?

9 Which method directly counts living cells that form colonies on solid medium?

10 What does increased turbidity in a bacterial culture usually indicate?

11 Which instrument is commonly used to measure the turbidity of a microbial culture?

12 Which method counts cells directly using a microscope and a special counting chamber?

13 Which temperature group grows best at moderate temperatures, such as those found in many human-associated environments?

14 What is the most favorable pH for most bacteria?

15 Which environmental factor refers to the availability of molecular oxygen for bacterial growth?

16 What is transformation in bacteria?

17 Which agent transfers bacterial DNA during transduction?

18 What is required for bacterial conjugation to occur?

19 Which structure commonly helps a bacterial cell transfer DNA during conjugation?

20 What type of DNA is commonly transferred during bacterial transformation?

21 A bacterial culture is transferred into fresh nutrient broth. During which phase are cells adapting to the new environment with little increase in cell number?

22 A culture has reached the stationary phase. Which change most likely explains why the total cell number remains nearly constant?

23 A bacterial population increases from cells to cells during exponential growth. How many generations have occurred?

24 A bacterial culture doubles every 30 minutes. Starting with 500 cells, approximately how many cells will be present after 2 hours during exponential growth?

25 Two bacterial species begin with equal populations. Species X has a generation time of 20 minutes, whereas Species Y has a generation time of 40 minutes. After 2 hours, which species will have the larger population?

26 A researcher wants most cells in a culture to divide at approximately the same time. Which method is most appropriate?

27 In a chemostat, fresh medium enters at the same rate that culture fluid leaves. What is the main consequence?

28 A continuous culture is diluted faster than the organism can reproduce. What is the most likely result?

29 A researcher needs to determine the number of viable bacteria in a milk sample. Which method is most suitable?

30 Why can turbidity measurements overestimate the number of living cells in a culture?

31 A sample is diluted , and mL produces 86 colonies. What is the original cell concentration?

32 Which measurement is most directly associated with estimating total microbial biomass rather than only viable cells?

33 A bacterium grows best at but stops growing at . How should it be classified by temperature preference?

34 An obligate anaerobe fails to grow in a culture tube exposed to air but grows at the bottom. Which explanation is most likely?

35 A bacterium grows poorly in a highly concentrated salt solution. Which effect most likely causes this reduced growth?

36 A bacterial species grows only between pH 6 and pH 8, with the fastest growth at pH 7. Which factor is being tested?

37 A nonpathogenic bacterium acquires DNA released from dead pathogenic cells and becomes pathogenic. Which process occurred?

38 A bacteriophage transfers a bacterial toxin gene from one bacterial cell to another. Which mechanism is responsible?

39 A bacterium transfers an antibiotic-resistance plasmid to a neighboring cell through direct contact using a sex pilus. Which process is this?

40 An F bacterium is mixed with an F bacterium under conditions that permit conjugation. What is the most likely outcome?

41 A bacterial culture has entered the stationary phase, but its optical density continues to increase slightly while viable counts decline. Which interpretation best explains this observation?

42 A culture increases from to cells per milliliter during exponential growth over 120 minutes. What is the generation time?

43 Two cultures begin with the same viable cell concentration. Culture A has a shorter lag phase but a lower exponential growth rate than culture B. If both are monitored until nutrients become limiting, which outcome is most likely?

44 A bacterial population doubles every 30 minutes during exponential growth. If the initial population is cells and the culture is incubated for 3 hours, what population is expected assuming no loss of viability?

45 A synchronous bacterial culture is produced by selecting cells at the same stage of the cell cycle. Why does its population eventually lose synchrony in a batch system?

46 In a chemostat operating at steady state, the dilution rate is increased above the organism's maximum specific growth rate. What is the immediate population-level consequence?

47 Two chemostats contain the same organism and limiting nutrient. The first has dilution rate and the second . At steady state, which statement is most defensible?

48 A researcher compares optical density with viable plate counts and finds that optical density rises while plate counts remain constant. Which explanation is most appropriate?

49 A culture is diluted 1:100, and of the dilution produces 86 colonies. What was the original viable cell concentration?

50 Which method would most directly distinguish metabolically active cells from intact but nonviable cells in a mixed bacterial suspension?

51 A facultative anaerobe grows throughout a thioglycollate tube but forms the densest growth near the surface. Which conclusion is best supported?

52 A halotolerant bacterium grows in both low- and high-salt media, but its growth rate decreases sharply at high salt concentration. Which classification is most accurate?

53 A bacterial enzyme has maximal activity at pH 7, but the organism grows best at pH 6. Which explanation best resolves this apparent contradiction?

54 A DNase-treated preparation of heat-killed donor bacteria fails to transform competent recipient cells, whereas an untreated preparation succeeds. What does this result demonstrate?

55 A competent recipient incorporates donor DNA containing an antibiotic-resistance allele, but the allele is not expressed until after several generations. Which event most likely occurred?

56 A bacteriophage transfers bacterial genes from many different chromosomal locations at low frequency, and the transferred genes are unrelated to the phage integration site. Which mechanism is indicated?

57 A temperate phage transfers only genes located adjacent to its chromosomal prophage insertion site after erroneous excision. Which prediction follows?

58 An Hfr donor transfers chromosomal genes to a recipient, but the recipient usually remains F−. Which explanation is most accurate?

59 A recipient becomes resistant to two antibiotics after mating with an F′ donor. The resistance genes are found on the transferred plasmid rather than integrated into the chromosome. What process best explains this result?

60 A conjugative plasmid is introduced into a recipient that already contains a closely related plasmid. The incoming plasmid is not stably maintained, even though transfer occurs. Which concept best explains this outcome?