Question 1

A student accidentally spills a culture of live bacteria on the lab bench. According to standard lab safety protocols, what is the FIRST action the student should take?

Accepted Answer

Cover the spill with paper towels soaked in disinfectant and inform the instructor immediately.

Question 2

Why is immersion oil used with the 100x objective lens on a compound light microscope?

Accepted Answer

To increase the numerical aperture and reduce light refraction, improving resolution.

Question 3

Which of the following best describes the arrangement of Streptococcus bacteria as seen under the microscope?

Accepted Answer

Chains of spherical cells

Question 4

During Gram staining, which chemical acts as the mordant, and what is its purpose?

Accepted Answer

Iodine; it forms a complex with crystal violet to help retain the dye in Gram-positive cells.

Question 5

A prepared slide shows a blue-green, filamentous organism with cells arranged in unbranched chains. Which cyanobacterium is most likely being observed?

Accepted Answer

Oscillatoria

Question 6

Which of the following best explains why Gram-positive and Gram-negative bacteria stain differently during the Gram stain procedure?

Accepted Answer

Differences in cell wall structure: Gram-positive bacteria have a thick peptidoglycan layer that retains crystal violet-iodine complex, while Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane.

Question 7

In the Schaeffer-Fulton spore staining method, why is steaming the slide for 5 minutes necessary?

Accepted Answer

To allow the primary stain (malachite green) to penetrate the tough spore coat.

Question 8

A student is preparing a bacterial smear from a solid medium. Which of the following steps is essential for proper smear preparation?

Accepted Answer

Mix a small amount of bacteria with a drop of water on the slide and air dry before heat fixing.

Question 9

Which of the following best describes the purpose of quadrant streaking in pure culture technique?

Accepted Answer

To isolate individual bacterial colonies from a mixed culture.

Question 10

A tube of semi-solid motility agar is stabbed with a bacterial culture. After incubation, growth is observed radiating away from the stab line. What does this indicate?

Accepted Answer

The organism is motile.

Question 11

Which of the following statements about the Ziehl-Neelsen acid-fast staining method is correct?

Accepted Answer

The primary stain is carbol fuchsin, and steaming is used to help the stain penetrate the waxy cell wall.

Question 12

Which substance is present in the cell wall of acid-fast bacteria and is responsible for their staining characteristics?

Accepted Answer

Mycolic acid

Question 13

A prepared slide shows a fungus with brush-like conidiophores and chains of asexual spores. Which organism is most likely being observed?

Accepted Answer

Penicillium

Question 14

Which of the following best distinguishes an obligate aerobe from a facultative anaerobe in a thioglycollate broth tube?

Accepted Answer

Obligate aerobes grow only at the top of the tube, while facultative anaerobes grow throughout but more densely at the top.

Question 15

Which of the following is the correct order of reagents used in the Gram staining procedure?

Accepted Answer

Crystal violet, iodine, alcohol, safranin

Question 16

A slide of Coprinus is observed under the microscope. Which reproductive structure should be identified to confirm it is a basidiomycete?

Accepted Answer

Basidiospores

Question 17

Which of the following best describes the appearance of a capsule stain under the microscope?

Accepted Answer

Clear halos surrounding dark-stained bacterial cells against a dark background

Question 18

Which of the following is a critical step in aseptic technique when transferring bacteria from a tube culture?

Accepted Answer

Flaming the mouth of the tube before and after inserting the loop

Question 19

Which of the following best describes the function of the condenser in a compound light microscope?

Accepted Answer

It focuses light onto the specimen to improve illumination.

Question 20

A prepared slide shows a sac-like structure containing eight spores. Which fungal reproductive structure is being observed, and which organism is it most likely from?

Accepted Answer

Ascospore from Pezziza

BIO 150 Microbiology Lab Exam Study Guide

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