Question 1

Which of the following best describes the role of carbohydrates in microbial fermentation?

Accepted Answer

Carbohydrates serve as energy sources and electron donors under anaerobic conditions.

Question 2

A microbiologist is testing an unknown bacterium in a liquid culture containing a carbohydrate and a pH indicator. After incubation, the medium turns yellow and a gas bubble is observed in the Durham tube. What does this indicate?

Accepted Answer

The bacterium fermented the carbohydrate, producing acid and gas.

Question 3

Which of the following statements about the use of pH indicators in fermentation tests is correct?

Accepted Answer

A pH indicator changes color in response to acid production from carbohydrate fermentation.

Question 4

During a fermentation test, the medium remains red and no gas is detected in the Durham tube after incubation. What is the most likely interpretation?

Accepted Answer

The microorganism did not ferment the carbohydrate.

Question 5

Which equation best represents the hydrolysis of ONPG by β-galactosidase?

Accepted Answer

$$\mathrm{ONPG} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{galactose} + \mathrm{ONP}$$

Question 6

Why is a Durham tube used in carbohydrate fermentation tests?

Accepted Answer

To detect the production of gas during fermentation.

Question 7

A student observes that a fermentation broth containing lactose and a pH indicator turns yellow but no gas is present in the Durham tube. What does this result suggest?

Accepted Answer

The microorganism fermented lactose, producing acid but not gas.

Question 8

Which of the following best explains why some microorganisms, such as E. coli, can use lactose as their sole source of carbon?

Accepted Answer

They possess the enzyme β-galactosidase, which hydrolyzes lactose into glucose and galactose.

Question 9

Which of the following is a common misconception about the fermentation of carbohydrates by microorganisms?

Accepted Answer

Fermentation always produces both acid and gas.

Question 10

In a laboratory test, a bacterium is inoculated into a medium containing ONPG and β-galactosidase. After incubation, a yellow color develops. What does this indicate?

Accepted Answer

ONPG was hydrolyzed, indicating β-galactosidase activity.

Question 11

Which of the following best describes the significance of using different carbohydrates in fermentation tests?

Accepted Answer

Different carbohydrates help identify microorganisms based on their fermentation patterns.

Question 12

A fermentation test medium contains a carbohydrate, a pH indicator, and a Durham tube. After incubation, the medium is yellow and the Durham tube contains a gas bubble. Which of the following equations best represents the overall process?

Accepted Answer

$$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 \rightarrow 2\ \mathrm{C}_2\mathrm{H}_5\mathrm{OH} + 2\ \mathrm{CO}_2$$

Question 13

Which of the following best explains why a pH indicator is essential in detecting carbohydrate fermentation?

Accepted Answer

It visually signals acid production resulting from fermentation.

Question 14

A microbiologist observes that a bacterium ferments glucose but not lactose. Which of the following is the most likely explanation?

Accepted Answer

The bacterium lacks the enzyme β-galactosidase.

Question 15

Which of the following is a correct interpretation if a fermentation broth turns yellow and the Durham tube is empty?

Accepted Answer

Acid was produced but no gas was formed during fermentation.

Fermentation of Carbohydrates in Microbiology

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