Question 1

Which of the following elements makes up the largest proportion of the dry weight of a bacterial cell?

Accepted Answer

Carbon (C)

Question 2

A microbiologist wants to culture a marine bacterium that requires sodium for growth. Which of the following media components should be included to support its growth?

Accepted Answer

Sodium chloride (NaCl)

Question 3

Which of the following best describes a defined medium?

Accepted Answer

A medium with an exact known chemical composition

Question 4

A researcher is using a spectrophotometer to measure microbial growth. What is the unit of measurement, and what does it represent?

Accepted Answer

Optical density (OD); turbidity due to light scattering by cells

Question 5

Which of the following statements about binary fission is correct?

Accepted Answer

It involves the formation of a septum that divides the cell

Question 6

A sample contains $$1 	imes 10^7$ cells/mL. After performing a ten-fold serial dilution three times, what is the final concentration of cells/mL in the last tube?

Accepted Answer

$$1 	imes 10^4$ cells/mL

Question 7

Which phase of the bacterial growth curve is characterized by the synthesis of new enzymes and adaptation to new conditions, but not an increase in cell number?

Accepted Answer

Lag phase

Question 8

Why do direct microscopic counts of natural samples often reveal more organisms than plate counts?

Accepted Answer

Many organisms have different growth requirements and do not grow on standard media

Question 9

Which of the following is a limitation of turbidimetric (optical density) measurements for estimating microbial cell numbers?

Accepted Answer

It cannot distinguish between live and dead cells

Question 10

A microbiologist wants to isolate a pure culture from a mixed sample. Which technique should be used to ensure isolation of single colonies?

Accepted Answer

Streak plate technique with an inoculating loop

Question 11

Which of the following best describes a selective medium?

Accepted Answer

A medium that contains compounds to inhibit the growth of some microbes but not others

Question 12

In a chemostat, which parameter is directly controlled by the dilution rate ($$D = F/V$$)?

Accepted Answer

The specific growth rate ($$k) of $$the culture

Question 13

Which of the following is a real-world application of viable plate counts?

Accepted Answer

Determining the number of Staphylococcus species in a water sample

Question 14

Which of the following statements about biofilms is correct?

Accepted Answer

Biofilms can cause medical device infections and industrial fouling

Question 15

Which macronutrient is primarily required for the synthesis of nucleic acids and phospholipids in microbial cells?

Accepted Answer

Phosphorus (P)

Question 16

A culture is in stationary phase. Which of the following best describes the state of the population?

Accepted Answer

Growth rate is zero due to nutrient depletion or waste accumulation

Question 17

Which of the following is a function of magnesium (Mg) in microbial cells?

Accepted Answer

Stabilizes ribosomes, membranes, and nucleic acids

Question 18

Which of the following best explains why colony-forming units (CFUs) are used instead of direct cell counts in plate counting methods?

Accepted Answer

CFUs account for clumps of cells that form a single colony

Question 19

Which of the following is a key difference between balanced growth by binary fission and budding cell division?

Accepted Answer

Binary fission results in nearly identical cells, while budding produces cells of different sizes

Microbial Growth and Its Control: Culturing, Nutrition, and Measurement

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