Q: Which of the following equations correctly represents the calculation for colony-forming units per milliliter (CFU/mL) when 0.1 mL of a 10⁻⁴ dilution yields 50 colonies on an agar plate?

$$\text{CFU/mL} = \frac{50}{0.1 \times 10$$^{-4}$$}$$

Question 1

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

Accepted Answer

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

Question 2

A researcher is growing a bacterial culture in a nutrient-rich broth. After several hours, the number of viable cells remains constant, but cell size increases. Which phase of the microbial growth curve is most likely being observed?

Accepted Answer

Lag Phase

Question 3

Which of the following equations correctly represents the calculation for colony-forming units per milliliter (CFU/mL) when 0.1 mL of a 10⁻⁴ dilution yields 50 colonies on an agar plate?

Accepted Answer

$$	ext{CFU/mL} = \frac{50}{0.1 	imes 10$$^{-4}$$}$$

Question 4

Which of the following is a key difference between passive and active transport in microbial nutrient uptake?

Accepted Answer

Active transport moves substances against a concentration gradient, while passive transport moves substances down a concentration gradient.

Question 5

A pathogenic bacterium produces siderophores during infection. What is the primary function of these molecules?

Accepted Answer

To bind and transport iron (Fe³⁺) into the bacterial cell

Question 6

Which of the following best explains why only plates with 30–300 colonies are considered statistically reliable in spread plating?

Accepted Answer

Fewer than 30 colonies increase the risk of sampling error, while more than 300 colonies lead to overcrowding and merging.

Question 7

Which of the following scenarios is an example of group translocation in bacteria?

Accepted Answer

A sugar molecule is phosphorylated as it is transported into the cell, preventing its diffusion back out.

Question 8

During the stationary phase of bacterial growth, which of the following is most likely to occur?

Accepted Answer

Cell division rate equals cell death rate, and stress response pathways are activated.

Question 9

Which of the following best describes the role of mineralization (ammonification) in the nitrogen cycle?

Accepted Answer

Breakdown of organic nitrogen compounds into ammonium (NH₄⁺), making nitrogen available to plants

Question 10

A microbe that uses carbon dioxide (CO₂) as its sole carbon source and obtains energy from inorganic chemical reactions is classified as which of the following?

Accepted Answer

Chemoautotroph

Question 11

Which of the following transport mechanisms is most likely responsible for the movement of oxygen (O₂) across a bacterial cell membrane?

Accepted Answer

Simple diffusion

Question 12

A laboratory technician is attempting to isolate a pure culture from a mixed bacterial sample. Which method should be used to achieve this goal?

Accepted Answer

Streak plate method on agar

Question 13

Which of the following best explains why some bacteria enter a Viable But Non-Culturable (VBNC) state during the death phase?

Accepted Answer

They are alive and metabolically active but cannot grow on standard laboratory media.

Question 14

Which of the following is a real-world example of secondary active transport in bacteria?

Accepted Answer

Import of lactose using a proton gradient established by ATP hydrolysis

Question 15

Which of the following best describes the function of ammonium transporters in microbial cells?

Accepted Answer

They facilitate the uptake of ammonium (NH₄⁺) into the cell from the environment.

Question 16

A microbiologist is cultivating an obligate anaerobe. Which of the following conditions must be provided for optimal growth?

Accepted Answer

Incubation in an anaerobic jar or chamber with no oxygen

Question 17

Which of the following statements about the streak plate method is correct?

Accepted Answer

It separates individual species from a mixed population to obtain pure colonies.

Question 18

Which of the following best explains why siderophore production is considered a virulence factor in pathogenic bacteria?

Accepted Answer

Siderophores allow bacteria to outcompete host proteins for iron, supporting growth and infection.

Microbial Nutrition, Growth, and Cultivation: Study Notes

Guida di studio - Domande di pratica

Study guide - Flashcard