Question 1

Which of the following best describes a macronutrient required by all microbes for growth?

Accepted Answer

Carbon, because it makes up about 50% of the dry weight of a microbial cell.

Question 2

A microbiologist wants to determine the minimal nutritional requirements for a newly discovered bacterium. Which type of medium should they use?

Accepted Answer

Defined medium, because the exact chemical composition is known.

Question 3

Which of the following statements about nitrogen utilization in microbes is CORRECT?

Accepted Answer

Ammonia ($$\mathrm{NH_3$}) is $$the most widely used nitrogen source among microbes.

Question 4

Which trace element is essential for the function of cytochrome c oxidases in microbial respiration?

Accepted Answer

Copper (Cu)

Question 5

A sample is plated on TCBS agar and produces yellow colonies. What is the most likely explanation?

Accepted Answer

The organism is likely Vibrio cholerae, which ferments sucrose and produces acid.

Question 6

Which of the following best explains why magnesium (Mg) is important for microbial cells?

Accepted Answer

It stabilizes ribosomes, membranes, and nucleic acids, and acts as an enzymatic cofactor.

Question 7

Which of the following is a distinguishing feature of complex media compared to defined media?

Accepted Answer

Complex media contain ingredients like yeast extract and peptone, making their composition variable.

Question 8

Which of the following best describes the role of sodium citrate and ox gall in TCBS agar?

Accepted Answer

They act as selective agents by inhibiting the growth of non-Vibrio bacteria.

Question 9

A marine bacterium requires sodium for growth but cannot grow in freshwater media. Which statement best explains this requirement?

Accepted Answer

Sodium is essential for some marine organisms due to their adaptation to saline environments.

Question 10

Which of the following best describes a heterotroph?

Accepted Answer

An organism that obtains carbon from organic molecules.

Question 11

Which growth factor is a precursor of NAD$$^+$$ and is required by some microbes?

Accepted Answer

Nicotinic acid (Niacin)

Question 12

Why might phosphorus be a limiting nutrient in some environments?

Accepted Answer

It is needed in large amounts for nucleic acids and phospholipids, but is often scarce.

Question 13

Which of the following best explains why TCBS agar is considered both selective and differential?

Accepted Answer

It inhibits non-Vibrio bacteria and distinguishes Vibrio species based on colony color.

Question 14

A researcher is trying to isolate a bacterium that requires vitamin B12 for growth. Which trace element should be included in the medium?

Accepted Answer

Cobalt (Co)

Question 15

Which of the following is a correct statement about the elemental composition of an E. coli cell?

Accepted Answer

Carbon is the most abundant element, comprising about 50% of the dry weight.

Question 16

Which of the following best describes the function of growth factors in microbial nutrition?

Accepted Answer

They are organic compounds required in small amounts for specific metabolic functions.

Question 17

A student prepares a medium with glucose, yeast extract, and peptone. Which type of medium is this?

Accepted Answer

Complex medium

Question 18

Which of the following is a reason why defined media are less commonly used for routine microbial cultivation?

Accepted Answer

They are expensive and time-consuming to prepare.

Question 19

Which of the following best explains why some Vibrio species form yellow colonies on TCBS agar?

Accepted Answer

They ferment sucrose, producing acid that lowers the pH and changes the dye color.

Question 20

Which of the following is a correct pairing of a trace element and its microbial function?

Accepted Answer

Iron (Fe): Component of cytochromes and nitrogenases

Microbial Nutrition, Media, and Cultivation: Essential Concepts for Microbiology

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