Question 1

Which of the following statements best describes the difference between defined and complex media used for microbial growth?

Accepted Answer

Defined media have a known exact chemical composition, while complex media contain digests of animal, plant, or microbial products with unknown composition.

Question 2

A microbiologist wants to count the number of viable cells in a milk sample. Which method should she use and why?

Accepted Answer

Viable plate count, because it measures only living, reproducing cells as colony-forming units.

Question 3

Which of the following is a major reason for the 'great plate count anomaly' in environmental microbiology?

Accepted Answer

Many microbes have specific growth requirements not met by standard laboratory media.

Question 4

A culture of E. coli is grown in a chemostat at steady state. Which parameter can be independently controlled to regulate the specific growth rate ($$k) of $$the culture?

Accepted Answer

The dilution rate ($$D = \frac{F}{V}$$), where $$F is $$flow rate and $$V is $$culture volume

Question 5

Which of the following best describes the exponential phase of a bacterial growth curve in batch culture?

Accepted Answer

Cells are doubling at regular intervals and are metabolically uniform.

Question 6

A sample contains $$1 	imes 10^8$ cells/mL. After performing a 10$$^{-4}$$ dilution and plating 1 mL, how many colonies would you expect to count if all cells are viable?

Accepted Answer

$$1 	imes 10^4$

Question 7

Which macronutrient is most directly required for the synthesis of nucleic acids and phospholipids in bacteria?

Accepted Answer

Phosphorus (P)

Question 8

Why is optical density (OD) measurement using a spectrophotometer not always an accurate indicator of viable cell number?

Accepted Answer

OD measurements cannot distinguish between live and dead cells, and clumping or biofilm formation can affect results.

Question 9

Which of the following is a key feature of biofilm growth that distinguishes it from planktonic growth?

Accepted Answer

Biofilm cells are enmeshed in a polysaccharide matrix and attached to a surface.

Question 10

A microbiologist is using a Petroff–Hausser counting chamber to estimate cell numbers. Which of the following is a limitation of this method?

Accepted Answer

It cannot distinguish between live and dead cells.

Question 11

Which trace metal is most commonly required as a cofactor for enzymes involved in cellular respiration and redox reactions?

Accepted Answer

Iron (Fe)

Question 12

During which phase of the bacterial growth curve does the population size remain constant due to a balance between cell division and cell death?

Accepted Answer

Stationary phase

Question 13

Which of the following best explains why aseptic technique is critical when transferring microbial cultures?

Accepted Answer

It ensures that only the desired microbe is transferred, preventing contamination from airborne or surface microbes.

Question 14

A researcher wants to maintain a bacterial culture in exponential phase for several weeks. Which system should she use?

Accepted Answer

Chemostat (continuous culture)

Question 15

Which of the following equations correctly represents the relationship between the number of generations ($$n$$), the initial number of cells ($$N_0$$), and the final number of cells ($$N) in $$exponential growth?

Accepted Answer

$$N = N_0$ 	imes 2^n$$

Question 16

Which of the following is NOT a typical application of the viable plate count method?

Accepted Answer

Counting viruses in a clinical sample

Question 17

Which of the following best describes the role of magnesium (Mg) in microbial cells?

Accepted Answer

It stabilizes ribosomes, membranes, and nucleic acids, and is required by many enzymes.

Question 18

Which of the following is a real-world consequence of biofilm formation?

Accepted Answer

Biofilms can foul and corrode pipes, and are implicated in medical device infections.

Question 19

Which of the following best describes the process of binary fission in bacteria?

Accepted Answer

A cell divides into two genetically identical daughter cells after elongation and septum formation.

Microbial Growth and Its Control – Study Notes

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