Q: A student is using a compound light microscope with a 10x ocular lens and a 40x objective lens. What is the total magnification being used, and which formula should be applied to calculate it?

Total magnification is 400x, calculated using $\text{Total Magnification} = \text{Ocular Magnification} \times \text{Objective Magnification}$

Question 1

A student is using a compound light microscope with a 10x ocular lens and a 40x objective lens. What is the total magnification being used, and which formula should be applied to calculate it?

Accepted Answer

Total magnification is 400x, calculated using $	ext{Total Magnification} = 	ext{Ocular Magnification} 	imes 	ext{Objective Magnification}$

Question 2

Which of the following best describes the purpose of the streak plate technique in microbiology?

Accepted Answer

To obtain isolated colonies from a mixed culture by diluting the sample across the surface of an agar plate

Question 3

After performing a Gram stain, a student observes purple cocci in clusters. What does this indicate about the bacterial cell wall structure and arrangement?

Accepted Answer

The bacteria are Gram-positive with a thick peptidoglycan layer and arranged in staphylococci clusters

Question 4

A microbiologist is preparing a bacterial smear for Gram staining. Which of the following steps is essential to ensure the cells adhere to the slide and are not washed away during staining?

Accepted Answer

Heat-fixing the smear by passing the slide through a flame

Question 5

During the citrate test, a bacterial culture turns the medium blue. What does this result indicate about the organism's metabolism?

Accepted Answer

The organism can utilize citrate as its sole carbon source, producing alkaline byproducts

Question 6

A student performs a urea hydrolysis test and observes a bright pink color in the medium. Which enzyme is responsible for this reaction, and what is being produced?

Accepted Answer

Urease; ammonia is produced, raising the pH

Question 7

In the S.I.M. test, a black precipitate forms in the medium. What does this indicate about the organism?

Accepted Answer

The organism reduces sulfur to hydrogen sulfide, which reacts with iron to form a black precipitate

Question 8

A phenol red broth test turns yellow after incubation with a bacterial culture. What does this result indicate about the metabolism of the bacteria?

Accepted Answer

The bacteria ferment the carbohydrate in the broth, producing acid and lowering the pH

Question 9

Which of the following best explains why mineral oil is added to the decarboxylation test medium?

Accepted Answer

To create an anaerobic environment that promotes decarboxylase enzyme activity

Question 10

A microbiologist is preparing a Kirby-Bauer test. Why is it important to create a bacterial lawn with a standardized inoculum before placing antibiotic disks?

Accepted Answer

To ensure even and consistent bacterial growth for accurate measurement of zones of inhibition

Question 11

A catalase test is performed by adding hydrogen peroxide to a bacterial colony. Bubbling is observed. What does this indicate about the organism?

Accepted Answer

The organism produces catalase, which breaks down hydrogen peroxide into water and oxygen

Question 12

A sample is plated on MacConkey agar and produces pink colonies. What does this indicate about the bacteria?

Accepted Answer

The bacteria are Gram-negative and ferment lactose, producing acid that turns the colonies pink

Question 13

Which of the following best describes the selective and differential properties of Mannitol Salt Agar (MSA)?

Accepted Answer

MSA is selective for Staphylococcus species due to high salt concentration and differential for mannitol fermentation, indicated by a yellow color change

Question 14

A blood agar plate shows clear zones around bacterial colonies. What type of hemolysis is this, and what does it indicate?

Accepted Answer

Beta-hemolysis; complete lysis of red blood cells

Question 15

A serial dilution is performed by transferring 100 µL from a tube with a dilution factor of $10^{-3}$ into a plate. The tube contains 1000 µL. What is the final dilution factor on the plate?

Accepted Answer

The final dilution factor is $10^{-4}$

Question 16

Which of the following best defines the term 'aseptic technique' in the microbiology laboratory?

Accepted Answer

A set of practices used to prevent contamination of cultures, the environment, and personnel

Question 17

Which of the following statements about fungi is correct?

Accepted Answer

Fungi are heterotrophic organisms that obtain nutrients by absorption, a strategy called saprotrophy

Question 18

A patient is diagnosed with malaria. Which protozoan is responsible for this disease, and what is the form that infects red blood cells?

Accepted Answer

Plasmodium species; the trophozoite form infects red blood cells

Question 19

Which of the following best describes the difference between a definitive host and an intermediate host in the life cycle of a helminth?

Accepted Answer

The definitive host harbors the adult, sexually reproducing stage, while the intermediate host harbors the larval or asexual stage

Question 20

A blood smear from a patient with acute myeloblastic leukemia is examined. Which leukocyte population is most likely to be elevated?

Accepted Answer

Myeloblasts (immature granulocytes)

Microbiology Lab Study Guide: Microscopy, Staining, Metabolic Tests, Selective Media, and Eukaryotic Microbes

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