Question 1

Which of the following best describes the process of nitrogen fixation in soil bacteria?

Accepted Answer

Conversion of nitrogen gas (N₂) into ammonia (NH₃) using specialized enzymes

Question 2

A bacterium living in a nutrient-poor aquatic environment must import glucose against its concentration gradient. Which transport mechanism is most likely used?

Accepted Answer

Primary active transport using ATP

Question 3

Which of the following equations correctly represents the doubling of a bacterial population during the log phase, where $N_0$ is the initial number of cells, $n$ is the number of generations, and $N$ is the final number of cells?

Accepted Answer

$N = N_0 	imes 2^n$

Question 4

Which of the following is a key difference between autotrophs and heterotrophs?

Accepted Answer

Autotrophs use CO₂ as a carbon source, while heterotrophs require organic molecules.

Question 5

During which phase of the microbial growth curve do cells adapt to a new environment and synthesize necessary enzymes, but do not increase in number?

Accepted Answer

Lag phase

Question 6

A microbiologist wants to count the number of viable bacteria in a water sample. After performing a ten-fold serial dilution and plating 0.1 mL of the $10^{-4}$ dilution, she counts 120 colonies. What is the original concentration of bacteria in CFU/mL?

Accepted Answer

$1.2 	imes 10^6$ CFU/mL

Question 7

Which of the following best explains why siderophores are important for bacterial pathogens during infection?

Accepted Answer

They allow bacteria to acquire iron from host proteins, overcoming nutritional immunity.

Question 8

Which process describes the breakdown of organic nitrogen from dead organisms into ammonium ($NH_4^+$) by microbes?

Accepted Answer

Mineralization (Ammonification)

Question 9

A bacterium is placed in a hypotonic solution. What is the most likely outcome if it lacks a cell wall?

Accepted Answer

It will lyse (burst) due to water influx.

Question 10

Which of the following is NOT a step in the classical Five I’s of microbial cultivation?

Accepted Answer

Immobilization

Question 11

Which of the following statements about passive transport in microbes is correct?

Accepted Answer

It includes osmosis, simple diffusion, and facilitated diffusion.

Question 12

Which of the following best describes group translocation in bacteria?

Accepted Answer

A nutrient is chemically modified as it enters the cell, preventing its exit.

Question 13

Why are only plates with 30–300 colonies considered statistically reliable for CFU counting?

Accepted Answer

Fewer than 30 colonies may result in high sampling error, and more than 300 colonies may lead to overcrowding and merging.

Question 14

Which of the following is a physiological adaptation bacteria may undergo during the stationary phase?

Accepted Answer

Activation of stress response pathways and production of secondary metabolites

Question 15

Which of the following best describes the role of ammonium transporters in microbial nitrogen assimilation?

Accepted Answer

They facilitate the uptake of ammonium ($NH_4^+$) into the cell, which is then incorporated into amino acids and nucleic acids.

Question 16

A pathogenic bacterium is unable to produce siderophores. What is the most likely consequence during infection?

Accepted Answer

It will have reduced ability to acquire iron and may be less virulent.

Question 17

Which of the following best explains why anaerobic bacteria require special cultivation conditions?

Accepted Answer

They are inhibited or killed by oxygen and must be grown in oxygen-free environments.

Question 18

Which of the following is a real-world application of microbial mineralization?

Accepted Answer

Release of ammonium ($NH_4^+$) from decomposing organic matter, making nitrogen available to plants

Question 19

Which of the following best describes the streak plate method in microbial isolation?

Accepted Answer

It separates individual species from a mixed population by diluting cells across an agar surface to produce discrete colonies.

Microbial Nutrition, Growth, and Development

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