Microbial Growth

Chapter 06 - Microbial Growth

Multiple Choice Questions

1. The total number of viable microorganisms remains constant in stationary phase because A. There is a balance between cell division and cell death B. There is a cessation of cell division even though the cells may remain metabolically active o r there is a cessation of cell C. Either there is a balance between cell division and cell death or division even though the cells may remain metabolically active D. None of the choices

2. Cells may enter stationary phase because of  A. The depletion of an essential nutrient B. A lack of available oxygen C. The accumulation of toxic waste products D. All of the choices

3. Which of these methods can be used to determine the number of viable microorganisms in a sample? A. Light scattering in a spectrophotometer  B. Measuring total cell mass C. Measuring colony forming units per ml D. Counting a known volume of cells in a hemocytometer 

4. A culture in a closed vessel to which no additional medium is added and from which no waste products are removed is called a __________ culture. A. Continuous B. Batch C. Fed-batch D. Semicontinuous

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5. Given a log phase bacterial culture with 106 cells per ml and a generation time of 30 minutes, how long does it take the culture to reach a density of 6.4 ´ 107 cells per ml? A. 1 hour  B. 2 hours C. 3 hours D. 4 hours

6. A culture system with constant environmental co nditions maintained through continual  provision of nutrient and removal of wastes is called __________ culture system. A. Continuous B. Batch C. Fed-batch D. Semicontinuous

7. An open system in which the growth rate is maintained by adding a nutrient (present in limiting quantities) at the same rate that medium containing microorganisms is removed is called A. Manostat B. Chemostat C. Turbidostat D. Culturostat

8. An open system in which the growth rate is maintained by the removal and addition of  media at such a rate as to maintain a constant cell density is called a A. Manostat B. Chemostat C. Turbidostat D. Culturostat

Chapter 06 - Microbial Growth

9. In an open culture system, the rate at which media is added and removed is called the  __________ rate. A. Dilution B. Chemostatic C. Pass-through D. Flow-through

10. The actin-like protein that seems to be involved in determining cell shape and chromosome movement is A. MreB B. ActA C. SpnC D. FtsZ

11. During cytokinesis, a critical step in septation is the assembly of the A. Replisome B. Spindle body C. Z ring D. Cytoskeletal spiral

12. Which of the following is considered a cardinal growth temperature? A. The minimum temperature B. The maximum temperature C. The optimum temperature D. All of these are considered cardinal growth temperatures

13. Organisms that grow well at 0 C and have optimum growth temperatures of 15 C or lower  are called A. Psychrotrophs B. Psychrophiles C. Frigiphiles D. Mesophiles °

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14. Organisms that grow well at 0 C to 7 C and have optimum growth temperatures between 20 C and 30 C are called A. Psychrotrophs B. Psychrophiles C. Frigiphiles D. Mesophiles °

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15. Organisms that do not require oxygen for growth but grow better in its presence are called A. Facultative anaerobes B. Microaerophiles C. Aerotolerant D. Anoxygenic

16. Organisms that ignore oxygen and grow equally well in its presence or absence are called A. Facultative anaerobes B. Microaerophiles C. Aerotolerant D. Anoxygenic

17. Organisms that are damaged by the normal atmospheric levels of oxygen (20%) but require oxygen at levels of 2–10% for growth are called A. Facultative anaerobes B. Microaerophiles C. Aerotolerant D. Anoxygenic

18. When a microorganism is placed in a(n) __________ solution, water will enter into the cell and cause it to burst unless something is done to prevent this. A. Hypotonic B. Isotonic C. Hypertonic D. Osmotonic

Chapter 06 - Microbial Growth

19. The membranes of psychrophilic bacteria have relatively high levels of __________ fatty acids, which allow them to remain semi-fluid at cold temperatures. A. Saturated B. Unsaturated C. Sterol D. Aromatic

20. Organisms that are not drastically affected by increased pressure are called A. Barotolerant B. Osmotolerant C. Barophilic D. Osmophilic

21. Organisms that require increased pressure for optimum growth are called A. Barotolerant B. Osmotolerant C. Barophilic D. Osmophilic

22. Most microorganisms maintain their internal pH A. Near neutral (pH 7) B. Near their optimum growth pH C. Slightly acidic (pH 4–6) D. Slightly alkaline (pH 8–10)

23. Microorganisms are most nearly uniform in terms of chemical a nd physiological  properties during __________ phase. A. Lag B. Exponential C. Stationary D. Decline

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24. Which of the following is a reason for the occurrence of a lag phase in a bacterial growth curve? A. The cells may be old and depleted of ATP, essential cofactors, and ribosomes that must be synthesized before growth can begin B. The medium may be different from the previous growth medium so that the cells must synthesize new enzymes to use different nutrients C. The organisms may have been injured and require time to recover  D. All of these are potential reasons

25. Which of the following is not used as a means used by bacteria to increase cell number: A. Fragmentation of filamentous cells B. Formation of endospores C. Formation of exospores D. Budding E. Binary fission

26. Which of the following can be used to estimate the number of microorganisms in a culture? A. Direct counts of microbial cells B. Counts of viable cells using colony growth procedures C. Measurements of microbial biomass D. All of the choices

27. At 4:00 p.m. a closed flask of sterile broth is inoculated with 10,000 cells. The lag phase lasts 1 hour. At 9:00 p.m. the log phase culture has population of 65 million cells. The approximate number of generations that has occurred is A. 5 B. 13 C. 21 D. 27

Chapter 06 - Microbial Growth

28. At 4:00 p.m. a closed flask of sterile broth is inoculated with 10,000 cells. The lag phase lasts 1 hour. At 9:00 p.m. the log phase culture has a population of 65 million cells. The mean generation time is approximately A. 10 minutes B. 20 minutes C. 30 minutes D. 40 minutes

29. At 4:00 p.m. a closed flask of sterile broth is inoculated with 10,000 cells. The lag phase lasts 1 hour. At 9:00 p.m. the culture enters stationary phase with a population of 65 million cells. At what time is the population half maximal? A. 6:30 p.m B. 7:20 p.m C. 8:20 p.m D. 8:40 p.m

30. Organisms that grow near deep-sea volcanic vents are likely to be A. Psychrophilic B. Psychrotrophic C. Mesophilic D. Thermophilic

31. Organisms that grow near deep-sea volcanic vents are likely to be A. Alkylophilic B. Acidophilic C. Barophilic or barotolerant D. Picrophilic

32. Organisms that grow in the mud under relatively nonturbulent bodies of water are likely to  be A. Obligate aerobes B. Thermophilic C. Barophilic D. Anaerobes

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33. The length of the lag phase of growth can vary depending on A. The condition of the microorganisms B. The nature of the growth medium C. The temperature D. All of the choices

34. Proposed functions of autoinducers include A. Gene regulation B. Sensing cell density C. Freely diffusing through the plasma membrane D. Two of the choices E. All of the choices

35. Quorum sensing A. Is a phenomenon in which bacteria monitor their own population density B. Depends on the sensing of signal molecules called autoinducers C. Plays an important role in formation of biofilms by Pseudomonas aeruginosa D. All of the choices

36. Membranes of thermophilic bacteria are stabilized b y phospholipids with A. Fatty acids that tend to be more saturated B. Fatty acids that have lower molecular weights C. Fatty acids that have more double bonds D. All of the choices

True / False Questions

37. One of the major advantages of a continuous culture system is that the cells can be maintained in the exponential growth phase for extended periods of time. TRUE

Chapter 06 - Microbial Growth

38. The primary mechanism by which DNA is damaged by ultraviolet radiation involves the formation of thymine dimers. TRUE

39. When a young, vigorously growing culture of bacteria is transferred to fresh medium of  the same composition, the lag phase is usually short or absent. TRUE

40. When a young, vigorously growing culture of bacteria is transferred to fresh medium of  different composition, the lag phase is usually short or absent. FALSE

41. Obligate anaerobes are usually poisoned by molecular oxygen but may grow in aerobic habitats if associated with facultative anaerobes that use up all available oxygen. TRUE

42. During the lag phase of microbial growth, the cells are metabolically inactive. FALSE

43. Membranes of some thermophilic Archaea are stabilized by lipids that span the membrane and form a rigid stable tetraether based monolayer. TRUE

44. The rate growth of a given species of microorganism is dependent on the composition of  the medium in which it is grown. TRUE

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45. Water activity is inversely proportional to osmotic pressure. TRUE

46. The most common types of autoinducers in gram-negative bacteria are acyl homoserine lactones (AHL). TRUE

47. DNA of thermophiles is stabilized by binding of special histone proteins. TRUE

48. Membranes of some thermophilic bacteria are stabilized by ether linked phospholipids. FALSE

Fill in the Blank Questions

49. Microbial __________ is an increase in cell constituents that may or may not be accompanied by an increase in cell number. growth

50. The ____________________ is the length of time it takes for a population of  microorganisms to double in number. generation time

51. Organisms that can grow in habitats with low water availability (high osmotic pressure)  by maintaining a high internal salt concentration are called __________ organisms. osmotolerant

Chapter 06 - Microbial Growth

52. Organisms that require high levels of sodium chloride in order to grow are called  __________ organisms. halophilic

53. Organisms that have their optimum growth pH between 0.0 and 5.5 are called  __________. acidophiles

54. Organisms that have their optimum growth pH between 5.5 and 8.0 are called  __________. neutrophiles

55. Organisms that have their optimum growth pH between 8.5 and 11.5 are called  __________. alkalophiles

56. If all cell components are synthesized at constant rates relative to one ano ther, the culture is said to be in __________ growth; however, if the rates of synthesis of some components change relative to the rates of synthesis of other components, the culture is said to be in  __________ growth. balanced; unbalanced

57. Growth is said to be __________ when all cellular components are synthesized at constant rates relative to one another. balanced

58. Organisms that grow best at pH levels above 10 are called ____________________. extreme alkalophiles

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59. Quorum sensing in Gram-positive bacteria generally involves the use of ____________ as the external signaling molecules. oligopeptides

60. Many microbes that live in environments where there is high exposure to light use  _______________ to provide protection from photoxidation by singlet oxygen. carotenoids

61. Complex microbial communities that grow tightly adhered to surfaces are called  __________. biofilms

62. Organisms with growth temperature maxima above 100 C are referred to as __________. hyperthermophiles °