Q: Which equation correctly represents the overall reaction catalyzed by urease?

$$\text{(NH}_2\text{)}_2\text{CO} + \text{H}_2\text{O} \rightarrow 2\text{NH}_3 + \text{CO}_2$$

Q: In the catalase test, what is the expected result for a catalase-positive organism, and what is the chemical reaction involved?

Bubbling due to release of O2; $$2\text{H}_2\text{O}_2 \rightarrow 2\text{H}_2\text{O} + \text{O}_2$$

Q: Which of the following best describes the role of denitrifying bacteria in the nitrogen cycle?

They convert nitrate ($$\text{NO}_3^-) to $$nitrogen gas ($$\text{N}_2$$), reducing nitrogen available to plants

Q: Which equation represents the sequence of nitrogen transformations during denitrification?

$$\text{NO}_3^- \rightarrow \text{NO}_2^- \rightarrow \text{NO} \rightarrow \text{N}_2\text{O} \rightarrow \text{N}_2$$

Question 1

Which color change in the urease test indicates rapid urease activity, and what is the underlying biochemical reaction?

Accepted Answer

Bright pink; rapid hydrolysis of urea to ammonia and CO2 increases pH

Question 2

A student performs a nitrate reduction test. After adding nitrate reagents A and B, the broth remains clear. After adding zinc powder, the broth turns red. What does this result indicate?

Accepted Answer

The bacteria did not reduce nitrate; nitrate is still present in the tube

Question 3

Which equation correctly represents the overall reaction catalyzed by urease?

Accepted Answer

$$	ext{(NH}_2	ext{)}_2	ext{CO} + 	ext{H}_2	ext{O} ightarrow 2	ext{NH}_3 + 	ext{CO}_2$$

Question 4

Which bacteria are most likely to test positive for rapid urease activity in a clinical setting?

Accepted Answer

Proteus vulgaris

Question 5

In the catalase test, what is the expected result for a catalase-positive organism, and what is the chemical reaction involved?

Accepted Answer

Bubbling due to release of O2; $$2	ext{H}_2	ext{O}_2 ightarrow 2	ext{H}_2	ext{O} + 	ext{O}_2$$

Question 6

Which of the following best describes the role of denitrifying bacteria in the nitrogen cycle?

Accepted Answer

They convert nitrate ($$	ext{NO}_3^-) to $$nitrogen gas ($$	ext{N}_2$$), reducing nitrogen available to plants

Question 7

A facultative anaerobic bacterium is grown in nitrate broth. After incubation, nitrate reagents A and B are added and the broth turns red. What does this indicate about the bacterium's metabolism?

Accepted Answer

It possesses nitrate reductase and can use nitrate as an electron acceptor during anaerobic respiration

Question 8

Which equation represents the sequence of nitrogen transformations during denitrification?

Accepted Answer

$$	ext{NO}_3^- ightarrow 	ext{NO}_2^- ightarrow 	ext{NO} ightarrow 	ext{N}_2	ext{O} ightarrow 	ext{N}_2$$

Question 9

Which of the following statements about the oxidase test is correct?

Accepted Answer

A positive result (blue color) indicates the presence of cytochrome c oxidase, which is involved in aerobic respiration

Question 10

Which bacteria would you expect to be catalase-negative based on the catalase test results and their metabolic characteristics?

Accepted Answer

Enterococcus faecalis

Question 11

A soil sample is tested for nitrogen-fixing bacteria. Which genus is most likely to be detected as a free-living nitrogen fixer?

Accepted Answer

Azotobacter

Question 12

Which step in the nitrate reduction test distinguishes between unreduced nitrate and nitrate reduced beyond nitrite?

Accepted Answer

Addition of zinc powder

Question 13

Why is the urease test particularly useful for identifying Proteus species among enteric bacteria?

Accepted Answer

Proteus hydrolyzes urea rapidly, causing a rapid pH increase and bright pink color

Question 14

Which of the following is a plausible consequence of overusing nitrogen fertilizers in agriculture?

Accepted Answer

Environmental damage due to excess nitrate runoff

Question 15

Which equation represents the reaction catalyzed by catalase?

Accepted Answer

$$2	ext{H}_2	ext{O}_2 ightarrow 2	ext{H}_2	ext{O} + 	ext{O}_2$$

Question 16

Which of the following bacteria would you expect to be oxidase-positive based on their respiratory characteristics?

Accepted Answer

Pseudomonas aeruginosa

Question 17

A patient sample is tested for catalase activity. The sample produces bubbles when hydrogen peroxide is added. What does this result suggest about the organism?

Accepted Answer

The organism is catalase-positive and can survive in oxygen-rich environments

Question 18

Which of the following best explains why only urease-positive bacteria can grow in urea broth?

Accepted Answer

Urea is the primary carbon and nitrogen source, so only bacteria that hydrolyze urea can obtain nutrients

Microbiology Lab: Urease, Nitrate Reduction, Catalase, and Oxidase Tests

Study Guide - Practice Questions

Study Guide - Flashcards