Total magnification $$= (10\times) \times (40\times) = 400\times$$

Question 1

Which of the following best describes the difference between selective and differential media?

Accepted Answer

Selective media allow only certain organisms to grow, while differential media distinguish between organisms based on biochemical reactions.

Question 2

A student prepares a slide by spreading bacteria, air drying, and then heat fixing. What is the main purpose of heat fixing in this procedure?

Accepted Answer

To kill the bacteria and adhere them to the slide.

Question 3

Which equation correctly calculates the total magnification when using a microscope with a 10X ocular lens and a 40X objective lens?

Accepted Answer

Total magnification $$= (10	imes) 	imes (40	imes) = 400	imes$$

Question 4

Which of the following best describes a fomite?

Accepted Answer

An inanimate object that can transmit infectious agents.

Question 5

A microbiologist wants to isolate a pure culture from a mixed sample. Which technique should they use and why?

Accepted Answer

Streak plate, because it separates individual cells to form isolated colonies.

Question 6

Which of the following is a correct interpretation of a Mannitol Salt Agar (MSA) plate showing yellow colonies?

Accepted Answer

The organism ferments mannitol, producing acid that turns the pH indicator yellow.

Question 7

Which group of organisms is inhibited by the agents in EMB and MAC plates?

Accepted Answer

Gram positive bacteria

Question 8

A TSI slant shows a yellow butt, yellow slant, and cracks in the agar. What does this indicate about the organism?

Accepted Answer

The organism ferments glucose, lactose and/or sucrose, and produces gas.

Question 9

Which pH indicator is commonly used in carbohydrate fermentation broth and TSI agar?

Accepted Answer

Phenol red

Question 10

Which of the following is a correct sequence for the Gram stain procedure?

Accepted Answer

Crystal violet, iodine, alcohol, safranin

Question 11

Which family of organisms does a TSI slant help to differentiate?

Accepted Answer

Enterobacteriaceae

Question 12

Which reagent is used to detect the presence of catalase in the catalase test?

Accepted Answer

Hydrogen peroxide ($$H_2O_2)$$

Question 13

A student observes bubbling after adding $$H_2O_2 to a $$bacterial colony. What does this result indicate?

Accepted Answer

The organism produces catalase, which breaks down $$H_2O_2$$ into water and oxygen.

Question 14

Which of the following best describes the role of oxidase in bacterial growth?

Accepted Answer

Oxidase is involved in the electron transport chain, facilitating aerobic respiration.

Question 15

Which flagellar arrangement describes a bacterium with a single flagellum at one end?

Accepted Answer

Monotrichous

Question 16

Which genera of Gram positive cocci are selected for by a MSA plate?

Accepted Answer

Staphylococcus

Question 17

A student performs a nitrate reduction test and observes a red color after adding reagents A and B. What does this result indicate?

Accepted Answer

Nitrate has been reduced to nitrite.

Question 18

Which of the following best describes an organism classified as a facultative anaerobe?

Accepted Answer

It can grow in both the presence and absence of oxygen.

Question 19

Which term describes a solution where the concentration of solutes is higher outside the cell than inside?

Accepted Answer

Hypertonic

Question 20

Which main families of organisms are acid-fast positive?

Accepted Answer

Mycobacteriaceae and Nocardiaceae

Microbiology Lab Midterm Review: Step-by-Step Study Guidance

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