Q: Which of the following equations correctly represents the calculation of colony-forming units per milliliter (CFU/mL) after spread plating?

$$\text{CFU/mL} = \frac{\text{Number of colonies}}{\text{Dilution factor} \times \text{Volume plated (mL)}}$$

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 microbiologist is culturing bacteria that require oxygen for growth. Which of the following incubation conditions is most appropriate?

Accepted Answer

Incubation in ambient air

Question 3

Which of the following equations correctly represents the calculation of colony-forming units per milliliter (CFU/mL) after spread plating?

Accepted Answer

$$	ext{CFU/mL} = \frac{	ext{Number of colonies}}{	ext{Dilution factor} 	imes 	ext{Volume plated (mL)}}$$

Question 4

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

Accepted Answer

Active transport moves substances against their concentration gradient, while passive transport moves substances down their concentration gradient

Question 5

A bacterium is found to secrete siderophores in an iron-limited environment. What is the primary function of these molecules?

Accepted Answer

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

Question 6

During which phase of the microbial growth curve do cells adapt to a new environment and prepare for division, but do not increase in number?

Accepted Answer

Lag phase

Question 7

Which of the following best explains why only plates with 30–300 colonies are considered statistically reliable for CFU counts?

Accepted Answer

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

Question 8

Which of the following transport mechanisms is used by bacteria to import glucose against its concentration gradient using energy from ATP?

Accepted Answer

Primary active transport

Question 9

A soil bacterium is able to use both organic and inorganic sources of carbon. Which term best describes its nutritional classification?

Accepted Answer

Mixotroph

Question 10

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

Accepted Answer

Breakdown of organic nitrogen compounds to release ammonium (NH₄⁺)

Question 11

A researcher observes that a bacterial culture has stopped increasing in cell number, but the cells remain metabolically active and begin producing antibiotics. Which phase of the growth curve is most likely being observed?

Accepted Answer

Stationary phase

Question 12

Which of the following is a real-world example of group translocation in bacteria?

Accepted Answer

Phosphorylation of glucose as it is transported into the cell

Question 13

Which of the following statements about osmosis in microbial cells is correct?

Accepted Answer

Osmosis is the movement of water from an area of low solute concentration to high solute concentration across a semi-permeable membrane

Question 14

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 bacterial growth during infection

Question 15

A microbiologist is using the streak plate method to isolate a pure culture. What is the primary goal of this technique?

Accepted Answer

To separate individual species from a mixed population by diluting cells across an agar surface

Question 16

Which of the following scenarios best illustrates the concept of nutritional immunity in the human body?

Accepted Answer

The body increases the production of transferrin to sequester iron and limit microbial growth

Question 17

Which of the following is a correct sequence of the Five I’s in microbial cultivation?

Accepted Answer

Inoculation, Incubation, Isolation, Inspection, Identification

Question 18

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

Accepted Answer

The cell will swell and may undergo lysis due to water influx

Question 19

Which of the following best describes the role of secondary active transport in microbial nutrient uptake?

Accepted Answer

It uses the energy stored in a proton gradient to transport nutrients

Question 20

During the death (decline) phase of the microbial growth curve, which of the following statements is true?

Accepted Answer

Cell death rate exceeds cell division rate, leading to a net decrease in viable cells

lec 06: Bacterial Culture, Growth, and Nutrient Acquisition: Microbiology Study Guide

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