Unit 1: Cell Counting - Practice Quiz

1 What is the main purpose of a Neubauer chamber?

2 What type of instrument is a Neubauer chamber?

3 What is the usual depth of the counting chamber under the coverslip?

4 Which instrument is used to observe cells in a Neubauer chamber?

5 Why is a coverslip placed on a Neubauer chamber?

6 What should be done before loading a yeast or bacterial suspension into the chamber?

7 What is the purpose of diluting a dense cell suspension?

8 If a sample is diluted tenfold, what is its dilution factor?

9 Which unit is commonly used to report yeast or bacterial concentration?

10 Why are several squares counted in a Neubauer chamber?

11 What should be done if the chamber contains too many cells to distinguish individually?

12 What should be done if very few cells are present in the counted squares?

13 What is the usual rule for cells touching the boundary lines?

14 What is the approximate volume above a mm² square with a chamber depth of mm?

15 What is the main reason for avoiding air bubbles when loading the chamber?

16 What does the average cell count represent?

17 If 40 cells are counted in 4 equal squares, what is the average count per square?

18 If the average count is 20 cells and the dilution factor is 5, which value increases the estimated original concentration?

19 Which cells should generally be counted as separate cells?

20 What should be recorded during a Neubauer chamber count?

21 A yeast suspension is diluted 1:10. The average count is 85 cells in each of five central Neubauer squares. Each square has a volume of . What is the cell concentration in the original suspension?

22 A bacterial sample is diluted 1:100, and 120 cells are counted in a Neubauer square measuring with a chamber depth of . What is the concentration in the original sample?

23 A student counts 48, 52, 50, and 54 yeast cells in four equivalent Neubauer squares. The sample was diluted 1:20, and each square has a volume of . What is the original concentration?

24 A yeast suspension gives an average of 64 cells per central square after a 1:5 dilution. If each counted square represents , how many cells are present in of the original suspension?

25 A student counts 75 cells in a square but forgets to apply a 1:4 dilution factor. The square volume is . What value will the student report, and what is the correct original concentration?

26 In a bacterial count, the following numbers are obtained from five squares: 31, 29, 30, 48, and 32. Which procedure is most appropriate before calculating the final concentration?

27 A diluted yeast sample has an average count of 40 cells per square. The square volume is , and the dilution factor is 25. What dilution would produce approximately 100 cells per square under the same conditions?

28 A cell lies exactly on the boundary between two Neubauer squares. Which counting rule reduces the risk of counting the same cell twice?

29 A yeast suspension is mixed with methylene blue. Among 200 total cells counted, 150 are unstained and 50 are blue. What are the viability and percentage of dead cells?

30 A student loads a Neubauer chamber without allowing the suspension to enter by capillary action. The cells are concentrated near the loading point. What is the most likely effect on the result?

31 A bacterial sample is diluted by mixing of culture with of diluent. What is the dilution factor of the resulting sample?

32 A student counts 90 cells in five central squares. Each square has a volume of . If the sample was diluted 1:10, what is the correct formula for the original concentration?

33 A yeast sample has an original concentration of . What dilution is needed to obtain approximately 80 cells in a square of volume ?

34 A student obtains 62, 64, 61, and 63 cells in four squares. Which reported average is most appropriate?

35 A bacterial suspension is too concentrated, and the cells overlap in the Neubauer chamber. What is the best corrective action?

36 A yeast suspension contains clumps, and each clump is counted as one unit. How will this usually affect the calculated cell concentration?

37 A student counts 56 cells in a square of volume after a 1:20 dilution. The sample was prepared by mixing of culture with of stain. What is the concentration in the original culture before staining?

38 A yeast count is performed in a chamber with a depth of . If the counting area is , what volume is represented by that area?

39 Two counts from the same bacterial sample are and . What is the mean concentration?

40 A student counts 25 bacteria in a square represented by after a 1:100 dilution. The sample is then diluted an additional tenfold before a second count. Approximately how many bacteria should be expected in the same square during the second count?

41 A yeast suspension is diluted 1:20 before loading. The four corner squares contain 82, 76, 79, and 83 cells. Assuming each corner square has a volume of , what is the original concentration?

42 Using the standard boundary convention for a Neubauer chamber, which cells should be included when counting a square?

43 A bacterial suspension diluted 1:100 gives a total of 125 bacteria in five central groups. Each group has an area of , and the chamber depth is . What was the concentration in the original suspension?

44 A sample is prepared by mixing of culture with of sterile diluent, followed by mixing of that suspension with of diluent. What is the final dilution relative to the original culture?

45 A yeast suspension is expected to contain approximately . If the desired mean count is about 50 cells in one large square of volume , which dilution should be prepared?

46 Four equivalent squares yield counts of 49, 51, 100, and 50 yeast cells. Which interpretation is most appropriate before calculating concentration?

47 If 400 bacterial cells are counted in a chamber volume and counting follows Poisson statistics, what is the approximate relative counting uncertainty caused by random sampling alone?

48 A chamber has a calibrated depth of , but it is accidentally loaded to a depth of . If the analyst still uses the nominal depth in the calculation, how is the concentration affected?

49 A bacterial count is made in five central groups, each measuring , with a chamber depth of . Which volume should be used for the five groups together?

50 A 1:1 mixture of yeast culture and viability stain produces a mean count of 72 viable cells per large square. The large-square volume is . What is the viable concentration in the original culture?

51 A yeast sample is diluted 1:25 and counted in four large squares. The counts are 62, 58, 61, and 59. Each square represents . What is the best estimate of the original concentration?

52 In the calculation described in the previous measurement, which value is the correct original concentration when the mean count is 60 cells, the square volume is , and the dilution is 1:25?

53 Two chambers are loaded from the same bacterial dilution. Chamber A gives 118 cells in five central groups, whereas chamber B gives 163 cells. Which conclusion is most defensible?

54 A researcher counts 24 bacteria in a five-group area and obtains a calculated concentration of . Which change would most improve precision without changing the sample concentration?

55 A yeast suspension contains many clumps, and each clump is recorded as one object. Compared with a properly dispersed suspension, what is the most likely result?

56 A bacterial dilution is prepared by adding of culture to of diluent. The diluted sample produces 90 bacteria in five central groups. What is the original concentration?

57 When counting bacteria in a central grid, an analyst counts the same boundary bacterium in two adjacent squares. What type of error has been introduced?

58 A student obtains 420, 18, and 2 cells in three serially diluted preparations. Which preparation is generally most suitable for a reliable Neubauer count, assuming the same counted volume?

59 A chamber is loaded with a bacterial suspension containing air bubbles. Counts from different regions vary from 35 to 110 cells. What is the best immediate response?

60 A yeast culture is counted after a 1:4 dilution. The mean count is 45 cells in a large square of volume . If the culture is intended to be seeded at , what volume of the original culture is required to prepare of inoculum?