Senior Secondary (HKDSE) · Biology

Microbiology: Practice Questions

5 multiple-choice questions marked as you go, and 4 written questions with worked solutions. All on Microbiology.

9 questions20 marksFree, no account

Question 1

1 mark

Which of the following statements best describes the multiplication of viruses?

Question 2

1 mark

In a microbiology laboratory, the growth of a yeast culture is monitored using turbidimetry (measuring the optical density of the culture). Which of the following is a major limitation of using this method to determine the number of viable cells in the culture during the death phase?

Question 3

1 mark

A student monitors the growth of a bacterial culture in a batch system. After the log phase, the growth rate slows down and the culture enters the stationary phase. Which of the following environmental changes is LEAST likely to be a primary cause for the onset of the stationary phase?

Question 4

1 mark

Which of the following substances is an essential carbon source for the aerobic respiration and growth of Saccharomyces cerevisiae (yeast) in a laboratory culture medium?

Question 5

1 mark

A microbiologist uses turbidimetry to estimate the growth of a yeast culture in a broth. If the culture is in the stationary phase, which of the following statements correctly compares the results of turbidimetry with a viable cell count performed via the spread-plate method?

Question 6

2 marks

State the primary reason why the mouth of a culture tube must be passed through a Bunsen flame immediately after opening and before closing it during a microbial transfer.

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Question 7

3 marks

Explain why the use of aseptic techniques is a fundamental principle when handling microbial cultures in a school laboratory.

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Question 8

5 marks

Explain the principle behind using antibiotics as a treatment for bacterial infections and why they are ineffective against viruses.

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Question 9

5 marks

A microbiologist monitored the growth of a bacterial population in a batch culture over 24 hours. The following data represents the number of viable cells recorded:
Time (h): 0, 4, 8, 12, 16, 20, 24
Viable count (\( \times 10^6 \) cells/mL): 2.0, 2.2, 8.5, 45.0, 46.0, 30.0, 15.0
(a) Based on the data provided, identify the time interval that corresponds to the exponential (log) phase.
(b) Account for the significant decrease in the viable cell count between 16 and 24 hours.
(c) If the microbiologist used turbidimetry to estimate the cell density at 24 hours, explain why the result might be higher than the actual viable count.

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