Question 1

Which part of the compound light microscope is responsible for focusing light onto the specimen and can be adjusted to increase or decrease the amount of light passing through the sample?

Accepted Answer

The iris diaphragm

Question 2

A student observes a bacterial cell under 1000x total magnification. The ocular ruler shows the cell is 5 ocular units long. If each ocular unit equals $$2 \ \mu m$$, what is the actual length of the cell?

Accepted Answer

$$10 \ \mu m$$

Question 3

Which of the following best describes the difference between prokaryotic and eukaryotic microorganisms as observed under a microscope?

Accepted Answer

Prokaryotes lack a membrane-bound nucleus, while eukaryotes have a membrane-bound nucleus.

Question 4

A microbiologist performs a Gram stain and observes purple, rod-shaped cells under the microscope. What can be concluded about the bacteria?

Accepted Answer

They are Gram-positive bacilli.

Question 5

Which staining technique is specifically used to identify bacteria with mycolic acid in their cell walls, such as Mycobacterium species?

Accepted Answer

Acid-fast stain

Question 6

During an endospore stain, what color will the endospores appear under the microscope if the procedure is performed correctly?

Accepted Answer

Green

Question 7

A student streaks a mixed bacterial culture on a nutrient agar plate using the streak plate technique. What is the primary purpose of this method?

Accepted Answer

To isolate individual colonies from a mixed culture

Question 8

Which of the following best describes a positive result in the catalase test?

Accepted Answer

Immediate bubbling upon addition of hydrogen peroxide

Question 9

A tube of phenol red glucose broth with a Durham tube is inoculated with a bacterium. After incubation, the broth turns yellow and a gas bubble is present in the Durham tube. What does this indicate about the bacterium?

Accepted Answer

It ferments glucose and produces gas.

Question 10

On Eosin-Methylene Blue (EMB) agar, a bacterial colony appears metallic green. What does this result indicate?

Accepted Answer

The bacterium is a strong lactose fermenter, likely Escherichia coli.

Question 11

Which enzyme is detected by the Spirit Blue Agar test, and what is a positive result?

Accepted Answer

Lipase; a clear zone around the colony

Question 12

A bacterium is inoculated into SIM medium. After incubation, the medium turns black. What does this indicate?

Accepted Answer

The bacterium produces hydrogen sulfide ($$H_2S).$$

Question 13

Which of the following best describes a positive result for the Simmons Citrate test?

Accepted Answer

The medium changes from green to blue.

Question 14

A microbiologist performs the Methyl Red test and observes a red color after adding methyl red indicator. What does this result indicate about the metabolic pathway used by the bacterium?

Accepted Answer

The bacterium performs mixed acid fermentation.

Question 15

Which of the following statements about the Gram stain procedure is correct?

Accepted Answer

Crystal violet is the primary stain, and safranin is the counterstain.

Question 16

A starch agar plate is flooded with iodine after incubation. A clear zone appears around the bacterial growth. What does this indicate?

Accepted Answer

The bacterium produces amylase, which hydrolyzes starch.

Question 17

Which of the following is a correct interpretation of a positive gelatin hydrolysis test?

Accepted Answer

The medium remains liquid after refrigeration, indicating gelatinase production.

Question 18

A decarboxylase test tube contains lysine and a pH indicator. After incubation, the medium turns purple. What does this result indicate?

Accepted Answer

The bacterium decarboxylates lysine, producing an alkaline product.

Question 19

Which of the following best describes the function of the Durham tube in a phenol red broth test?

Accepted Answer

To detect gas production during fermentation

Question 20

A patient sample is tested for coliforms using phenol red lactose broth with a Durham tube. After incubation, the broth is yellow and the Durham tube contains a gas bubble. What does this result suggest about the sample?

Accepted Answer

Coliforms are present, indicating possible fecal contamination.

General Microbiology Lab Exam 1 Study Guide

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