Question 1

Which of the following best describes a defined (synthetic) culture medium?

Accepted Answer

A medium in which the exact chemical composition is known.

Question 2

A microbiologist wants to count only living bacteria in a water sample. Which method should they use?

Accepted Answer

Viable plate count method

Question 3

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

Accepted Answer

Phosphorus

Question 4

A bacterium that uses organic carbon sources for growth is classified as a:

Accepted Answer

Heterotroph

Question 5

Which of the following statements about turbidimetric measurement of microbial growth is correct?

Accepted Answer

It measures the optical density of a cell suspension, which is proportional to cell number.

Question 6

Why is serial dilution necessary before performing a viable plate count on a dense bacterial culture?

Accepted Answer

To obtain countable plates with 30-300 colonies

Question 7

Which trace element is most commonly required as a cofactor for redox enzymes in bacteria?

Accepted Answer

Iron (Fe)

Question 8

A researcher is using a streak plate technique to isolate a pure culture. What is the main purpose of this technique?

Accepted Answer

To separate individual microbial cells so that they grow into isolated colonies

Question 9

Which of the following best explains why direct microscopic counts may overestimate the number of viable bacteria in a sample?

Accepted Answer

They count both live and dead cells.

Question 10

Which equation correctly represents the relationship between optical density (OD) and cell concentration in a turbidimetric assay?

Accepted Answer

$OD = k 	imes N$

Question 11

A bacterium is able to grow using ammonia ($NH_3$) as its sole nitrogen source. Which macromolecule is most directly synthesized from this nitrogen source?

Accepted Answer

Proteins

Question 12

Which of the following is a limitation of the viable plate count method?

Accepted Answer

It may underestimate the number of cells if some bacteria cannot grow on the medium used.

Question 13

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

Accepted Answer

It stabilizes ribosomes, membranes, and nucleic acids.

Question 14

A microbiologist is preparing a complex medium. Which of the following ingredients would most likely be included?

Accepted Answer

Yeast extract

Question 15

Which of the following statements about binary fission in bacteria is correct?

Accepted Answer

It results in two genetically identical daughter cells.

Question 16

Which of the following is a function of growth factors in microbial nutrition?

Accepted Answer

They serve as organic micronutrients required for enzyme function.

Question 17

A sample contains $1 	imes 10^7$ cells/mL. After performing a 1:100 dilution and plating 0.1 mL, how many colonies would you expect to count if all cells are viable?

Accepted Answer

10,000

Question 18

Which of the following best explains why some bacteria require trace metals for growth?

Accepted Answer

Trace metals act as cofactors for enzymes involved in catalysis.

Question 19

Which of the following is a key advantage of using turbidimetric measurements to estimate microbial cell numbers?

Accepted Answer

It is rapid and does not require sample destruction.

Question 20

A microbiologist is studying a bacterium that can use both nitrate ($NO_3^-$) and ammonia ($NH_3$) as nitrogen sources. Which of the following best describes this organism's nutritional flexibility?

Accepted Answer

It can assimilate nitrogen from both inorganic and organic sources.

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

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