Q: Which formula correctly expresses the limit of resolution ($d$) for a light microscope?

$d = \frac{0.5 \times \lambda}{NA}$

Question 1

Which of the following best describes the purpose of using aseptic technique in microbiology laboratories?

Accepted Answer

To prevent contamination of the microbial sample and protect the worker from infection.

Question 2

When using a compound light microscope, what is the main function of the condenser?

Accepted Answer

To focus light onto the specimen for improved resolution.

Question 3

A student is preparing a wet mount of pond water to observe bacteria. Which of the following steps is essential to avoid introducing air bubbles under the coverslip?

Accepted Answer

Lower the coverslip slowly at an angle onto the drop of water.

Question 4

Which formula correctly expresses the limit of resolution ($d$) for a light microscope?

Accepted Answer

$d = \frac{0.5 	imes \lambda}{NA}$

Question 5

Why is it important to flame the mouth of a test tube when opening and closing it during aseptic transfer?

Accepted Answer

To prevent airborne contaminants from entering the tube.

Question 6

A microbiologist is using a bright-field microscope to observe unstained bacteria. What is the main limitation of this approach?

Accepted Answer

Unstained bacteria have low contrast with the background, making them difficult to see.

Question 7

During a plate pouring procedure, which of the following actions best demonstrates proper aseptic technique?

Accepted Answer

Opening petri dish lids only briefly and keeping them close to the flame.

Question 8

Which part of the compound light microscope is responsible for magnifying the image after it passes through the objective lens?

Accepted Answer

Ocular (eyepiece)

Question 9

A student accidentally spills a small amount of bacterial culture on the bench. According to laboratory safety procedures, what is the correct immediate response?

Accepted Answer

Cover the spill with disinfectant and clean after a few minutes.

Question 10

Which of the following best explains why oil immersion is used with the 100x objective lens in light microscopy?

Accepted Answer

Oil reduces light refraction, allowing more light to enter the lens and improving resolution.

Question 11

A scientist wants to observe motility in live bacteria. Which sample preparation method is most appropriate?

Accepted Answer

Wet mount

Question 12

Which of the following is a critical step when using a metal inoculating loop for transferring bacteria?

Accepted Answer

Sterilize the loop by flaming until red hot before and after use.

Question 13

If the numerical aperture ($NA$) of an objective lens is 1.25 and the wavelength ($\lambda$) of light used is 500 nm, what is the theoretical limit of resolution ($d$) for the microscope?

Accepted Answer

$d = \frac{0.5 	imes 500}{1.25} = 200$ nm

Question 14

Which of the following is NOT a recommended practice for minimizing contamination when working with microbial samples?

Accepted Answer

Placing used loops directly on the workbench.

Question 15

A student is using a microscope with a 10x ocular lens and a 40x objective lens. What is the total magnification?

Accepted Answer

$10 	imes 40 = 400$

Question 16

Which of the following statements about sterilization of media is correct?

Accepted Answer

Heat-sensitive media are sterilized by filtration.

Question 17

Why is it important to avoid vigorous shaking of a specimen prior to opening the container?

Accepted Answer

It increases the risk of aerosol formation and potential exposure.

Question 18

Which of the following best describes the function of the stage on a compound light microscope?

Accepted Answer

Holds and supports the specimen slide for observation.

Question 19

A researcher is counting bacteria using a haemocytometer. What is the main advantage of this method?

Accepted Answer

It allows for direct counting of live and dead cells.

Question 20

Which of the following is a reason for using plasticware instead of glassware in modern microbiology labs?

Accepted Answer

Plasticware reduces the risk of breakage and accidental spills.

Aseptic Technique and Microscopy in Microbiology: Principles and Laboratory Practice

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