Q: A bacterium is inoculated into a phenol red lactose broth. After incubation, the broth is yellow and contains a gas bubble in the Durham tube. Which of the following equations best represents the fermentation process occurring?

$$C_6H_{12}O_6$ \rightarrow 2C_2H_5OH + 2CO_2 + \text{acid}$$

Question 1

Which of the following best describes the metabolic process occurring in a bacterium that produces a yellow color in both the sealed and unsealed tubes of an O-F glucose test (as seen in Pair 4 of the first image)?

Accepted Answer

The bacterium is capable of both oxidative and fermentative metabolism of glucose.

Question 2

In the phenol red broth test, what does a yellow color with a gas bubble in the Durham tube (as seen in the first tube of the second image) indicate about the metabolic activity of the organism?

Accepted Answer

The organism ferments the carbohydrate, producing acid and gas.

Question 3

A clear zone around bacterial growth on a starch agar plate after the addition of iodine (as seen in the right side of the third image) indicates which enzymatic activity?

Accepted Answer

The bacterium produces amylase, which hydrolyzes starch.

Question 4

Which of the following best explains the clearing observed around bacterial growth on a milk agar plate (as seen in the fourth image)?

Accepted Answer

The bacterium produces casease, which hydrolyzes casein in the milk.

Question 5

A student observes a phenol red broth tube that is pink after incubation (as seen in the last tube of the second image). What does this result indicate?

Accepted Answer

The organism deaminated peptone, raising the pH above 7.4.

Question 6

Which of the following statements about hydrolytic enzymes is correct?

Accepted Answer

Amylase is an extracellular enzyme that hydrolyzes starch into smaller subunits.

Question 7

In the O-F glucose test, what is the purpose of adding mineral oil to one of the tubes?

Accepted Answer

To create an anaerobic environment and test for fermentative metabolism.

Question 8

A bacterium is inoculated into a phenol red lactose broth. After incubation, the broth is yellow and contains a gas bubble in the Durham tube. Which of the following equations best represents the fermentation process occurring?

Accepted Answer

$$C_6H_{12}O_6$ ightarrow 2C_2H_5OH + 2CO_2 + 	ext{acid}$$

Question 9

Which of the following best explains why starch must be hydrolyzed before it can be utilized by most bacteria?

Accepted Answer

Starch is too large to cross the cell membrane and must be broken down into smaller subunits.

Question 10

A milk sample is tested for bacterial contamination using a casease test. After 24 hours, a clear zone appears around the bacterial growth. What does this result indicate about the bacteria present?

Accepted Answer

The bacteria can hydrolyze casein and are likely to be found in dairy products.

Question 11

Which of the following is a distinguishing feature of Enterobacteriaceae in the phenol red broth test?

Accepted Answer

They ferment glucose, often producing both acid and gas.

Question 12

A bacterium is inoculated onto a tributyrin agar plate. After incubation, a clear zone is observed around the growth. What does this indicate?

Accepted Answer

The bacterium produces lipase, which hydrolyzes triglycerides.

Question 13

Which of the following best describes the role of the electron transport chain in aerobic respiration?

Accepted Answer

It transfers electrons to oxygen, the final electron acceptor, generating ATP.

Question 14

A student performs an O-F glucose test and observes that only the unsealed tube turns yellow while the sealed tube remains green. What is the most likely metabolic characteristic of the organism?

Accepted Answer

The organism is strictly oxidative and cannot ferment glucose.

Question 15

Which of the following is a correct statement about the use of pH indicators in biochemical tests?

Accepted Answer

Phenol red turns yellow at pH \u003c 6.8, indicating acid production.

Question 16

Which of the following best explains the difference between intracellular and extracellular hydrolytic enzymes?

Accepted Answer

Extracellular enzymes are secreted to break down large molecules outside the cell, while intracellular enzymes function within the cell.

Question 17

A bacterium is tested in a phenol red sucrose broth. After incubation, the broth is red and there is no gas in the Durham tube. What is the correct interpretation?

Accepted Answer

The organism did not ferment sucrose and did not produce gas.

Question 18

Which of the following is a likely consequence of a bacterium lacking extracellular hydrolytic enzymes such as amylase, casease, and lipase?

Accepted Answer

It would be unable to utilize large polymers like starch, casein, or triglycerides as nutrient sources.

Question 19

Which of the following best describes the metabolic pathway of fermentation?

Accepted Answer

Glucose is the electron donor and its organic products are the electron acceptors.

Question 20

A patient sample is tested for the presence of lipolytic bacteria using a tributyrin plate. After incubation, no clearing is observed around the bacterial growth. What does this result suggest?

Accepted Answer

The bacteria do not produce lipase and cannot hydrolyze triglycerides.

Biochemical Tests for Microbial Metabolism and Hydrolysis

Study Guide - Practice Questions

Study Guide - Flashcards