Q: Which of the following is the correct formula to calculate total magnification on a compound microscope?

$$\text{Total Magnification} = \text{Objective Lens Magnification} \times \text{Ocular Lens Magnification}$$

Question 1

You just sliced your finger with a piece of broken glass in the microbiology lab. What is the FIRST thing you should do?

Accepted Answer

Immediately notify your instructor and follow the lab's injury protocol.

Question 2

Why do we remove our lab coats when leaving the laboratory area (e.g., to go to the bathroom or hallway)?

Accepted Answer

To prevent the spread of laboratory contaminants to public areas.

Question 3

Which of the following is the correct formula to calculate total magnification on a compound microscope?

Accepted Answer

$$	ext{Total Magnification} = 	ext{Objective Lens Magnification} 	imes 	ext{Ocular Lens Magnification}$$

Question 4

Immersion oil is used with which objective lens, and why is it necessary?

Accepted Answer

100X; to reduce light refraction and improve resolution.

Question 5

Which of the following best describes the purpose of heat fixing a bacterial smear before staining?

Accepted Answer

To kill the bacteria and adhere them to the slide.

Question 6

What are the standard autoclave conditions for sterilizing media?

Accepted Answer

$$121\ ^\circ\mathrm{C}$$, 15 psi, 15-20 minutes

Question 7

Why do we temper agar media before pouring plates?

Accepted Answer

To prevent condensation and avoid killing heat-sensitive additives.

Question 8

Which metabolic pathway does glyphosate inhibit in sensitive microorganisms?

Accepted Answer

Shikimate pathway

Question 9

A catalase test is performed on a bacterial colony. Bubbling is observed after adding hydrogen peroxide. What does this indicate?

Accepted Answer

The organism produces catalase and breaks down $$\mathrm{H}_2\mathrm{O}_2$$ into $$\mathrm{H}_2\mathrm{O}$$ and $$\mathrm{O}_2.$$

Question 10

Which of the following best describes the difference between sterile and aseptic techniques?

Accepted Answer

Sterile means completely free of all living organisms; aseptic means preventing contamination by unwanted organisms.

Question 11

You are making 10 mL of media that needs to be 3% acetate and 0.5% ammonium chloride. Your stock solutions are 15% acetate and 13% ammonium chloride. How much of each stock solution do you need to add? (Show the formula used.)

Accepted Answer

Use $$V_1$$ = \frac{C_2V_2}{$$C_1$$}$$ for each: V$$_{acetate} = \frac{3\% 	imes 10\ \mathrm{mL}}{15\%} = 2\ \mathrm{mL}$$; V$$_{NH_4Cl} = \frac{0.5\% 	imes 10\ \mathrm{mL}}{13\%} \approx 0.385\ \mathrm{mL}$$

Question 12

Which of the following best explains why colony-forming units (CFUs) are used to estimate the number of viable cells in a sample?

Accepted Answer

Each CFU arises from a single viable cell capable of forming a colony.

Question 13

Which of the following best describes the difference between a common source epidemic and a host-to-host epidemic, as shown in the provided graph?

Accepted Answer

A common source epidemic shows a sharp rise and fall in cases, while a host-to-host epidemic shows a gradual increase and decrease.

Question 14

Which of the following is a reason for parafilming plates in microbiology labs?

Accepted Answer

To prevent contamination and reduce evaporation.

Question 15

Which of the following best describes the purpose of using selective and differential media in microbiology?

Accepted Answer

Selective media inhibit the growth of some organisms while allowing others to grow; differential media distinguish between organisms based on biochemical reactions.

Question 16

Which of the following is the correct formula to calculate the molarity (mM) of acetate in a solution if you have 3% (w/v) acetate and the molecular weight is 60.052 g/mol?

Accepted Answer

$$	ext{Molarity (M)} = \frac{	ext{grams of solute}}{	ext{molecular weight} 	imes 	ext{volume in liters}}$$

Question 17

Which of the following best describes why not all strains of Escherichia coli are pathogenic?

Accepted Answer

Only strains that produce specific toxins, such as Shiga toxin, are pathogenic.

Question 18

Which of the following best describes the role of microbiota in humans?

Accepted Answer

Microbiota are the community of microorganisms living in and on the human body, providing benefits such as protection against pathogens and aiding digestion.

Microbiology Lab Practical Study Guide: Step-by-Step Guidance

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