Unit 9: Microbial biotechnology I - Practice Quiz

1 What is the primary function of the enzyme cellulase?

2 Cellulose is composed of repeating units of which sugar?

3 Which natural environment is a rich source of cellulose-degrading microorganisms?

4 Which carbon source is commonly used in media to isolate cellulase producers?

5 Which dye is commonly used to detect cellulase activity on CMC agar plates?

6 The clear zone around a colony on a Congo red stained CMC plate indicates:

7 Which technique is commonly used to obtain isolated colonies from a soil sample?

8 Why is serial dilution performed before plating a soil sample?

9 A microorganism that can degrade cellulose is termed:

10 Which of the following is a well-known fungal producer of cellulase?

11 The medium used to isolate only cellulase producers is best described as:

12 During screening, cellulase activity is often visualized by flooding plates with Congo red followed by washing with:

13 Cellulose is the main structural component of which of the following?

14 Which product is released when cellulase completely hydrolyzes cellulose?

15 For measuring cellulase activity, the ratio of clear zone diameter to colony diameter is called the:

16 Before isolating microbes, the glassware and media used must be:

17 Which equipment is commonly used to sterilize media by moist heat?

18 After plating, inoculated plates are kept in an incubator mainly to provide:

19 Which bacterial genus is a common cellulase producer isolated from soil?

20 Cellulases have important industrial applications in which of the following?

21 A researcher wants to isolate cellulase-producing microbes from a soil sample. Which soil source is most likely to yield a high number of cellulolytic organisms?

22 Carboxymethyl cellulose (CMC) agar is commonly used as a selective medium in cellulase screening. What is the primary role of CMC in this medium?

23 After growing colonies on CMC agar, the plate is flooded with Congo red and then washed with 1 M NaCl. What does a clear zone (halo) around a colony indicate?

24 Two isolates form clear zones on CMC agar. Isolate A has a colony diameter of 5 mm with a halo diameter of 20 mm; Isolate B has a colony of 8 mm with a halo of 16 mm. Which isolate has the higher hydrolysis capacity (HC) value?

25 The serial dilution technique is used before plating soil suspensions. What is the main purpose of performing serial dilutions?

26 During enrichment culture for cellulase producers, filter paper strips are added to a liquid mineral medium instead of glucose. Why is filter paper preferred here?

27 A student observes that filter paper strips in an enrichment flask become soft, frayed, and eventually disintegrate over several days. What does this observation best suggest?

28 Which combination of enzymes constitutes the complete cellulase system needed for full cellulose degradation by isolated microbes?

29 When preparing a soil suspension for isolation, why is the soil typically mixed with sterile saline (0.85% NaCl) rather than distilled water?

30 A soil sample is diluted to and 0.1 mL is spread on a plate, yielding 48 colonies. What is the estimated cell count per gram of the original soil?

31 Why is Congo red staining preferred over simply observing colony growth on CMC agar when screening for cellulase producers?

32 Which genus is a well-known fungal cellulase producer frequently isolated from soil in laboratory studies?

33 To confirm and purify a promising cellulase-producing isolate showing a clear halo, the next logical step is to:

34 A quantitative cellulase assay using the DNS (3,5-dinitrosalicylic acid) method measures which product to estimate enzyme activity?

35 Why might a screening plate incubated with glucose-containing CMC agar give misleading results for cellulase detection?

36 The spread plate method is used to distribute a diluted soil sample evenly over the agar surface, which is the reason why this technique is well-suited for isolating aerobic cellulase producers that require good oxygen exposure and surface growth to form measurable clearing zones. Which statement about the pour plate method, in contrast, is correct?

37 For isolating thermophilic cellulase producers from compost soil, incubation is best carried out at:

38 Which control should be included on a CMC-Congo red screening plate to validate that observed halos are due to enzymatic hydrolysis?

39 A soil isolate grows on CMC agar but shows no clear zone after Congo red staining. The most reasonable interpretation is that the isolate:

40 When storing a confirmed cellulase-producing bacterial isolate for long-term preservation, which method best maintains viability and genetic stability?

41 During screening on carboxymethyl cellulose (CMC) agar, two isolates produce identical clear zone diameters after Congo red staining, but Isolate A shows a much smaller colony diameter than Isolate B. Which conclusion about relative cellulolytic efficiency is most defensible?

42 Congo red binds to -1,4-glucan polymers but not to their hydrolysis products. Why does this property make it suitable for visualizing cellulase activity on CMC plates?

43 A researcher performs serial dilution of a soil suspension and plates from the dilution, obtaining 148 colonies. What is the CFU per gram of the original soil sample?

44 An enrichment culture uses cellulose as the sole carbon source. After several transfers, a fast-growing non-cellulolytic organism dominates the culture. What is the most likely explanation?

45 Why is CMC (a soluble cellulose derivative) preferred over microcrystalline cellulose (Avicel) for primary plate screening of cellulase producers?

46 A colony hydrolyzes CMC (endoglucanase-positive) but shows no activity on filter paper. What does this most likely indicate about its cellulase system?

47 In a DNS (dinitrosalicylic acid) assay for cellulase activity, one unit is defined as the enzyme releasing of reducing sugar per minute. If enzyme releases glucose equivalents in a 30-minute reaction, what is the activity in U/mL?

48 Soil samples from a forest floor rich in decaying leaf litter are chosen preferentially for cellulase producer isolation. What is the ecological rationale?

49 A student stains a CMC plate with Congo red for 15 minutes, then observes weak, poorly defined halos. Adding a counterstain wash sharpens the zones dramatically. Why?

50 Two isolates have enzymatic indices of and on CMC plates, yet secondary DNS liquid assays show markedly different total cellulase activities. What best explains this discrepancy?

51 In an isolation medium, the sole nitrogen source is and the sole carbon source is cellulose. If cellulose degradation is slow, which limiting factor most directly restricts cellulase producer growth?

52 A dense soil suspension is plated without adequate dilution, producing confluent growth and merged halos on CMC agar. What is the most rigorous corrective step for accurate screening?

53 Why might a genuinely cellulolytic fungal isolate produce a large clear zone yet grow poorly when cellulose is the sole carbon source, whereas a bacterial isolate grows robustly?

54 When calculating cellulase specific activity, which expression is correct?

55 A soil suspension is heat-treated at for 15 minutes before plating for cellulase producers. What is the primary intent, and what is a key limitation?

56 In a DNS assay, absorbance is read at against a glucose standard curve with slope and intercept . If sample absorbance is , the reducing sugar concentration is best given by:

57 A newly isolated strain shows a large halo on CMC agar but the halo does not increase after 48 h even though the colony keeps growing. What is the most likely interpretation?

58 Which combination of controls is essential to validate that a clear zone on a Congo red CMC plate is genuinely due to enzymatic cellulose hydrolysis?

59 During optimization, a producer's cellulase activity drops sharply when glucose is added to the medium alongside cellulose. What regulatory phenomenon best explains this?

60 Comparing two isolates: Isolate X gives zone/colony diameters of and Isolate Y gives . Based on enzymatic index, which is the better candidate and why?