Question 1

The purpose of a mordant in the Gram stain is to

Accepted Answer

The purpose of a mordant in the Gram stain is to bind the crystal violet stain to the peptidoglycan layer of the bacterial cell wall, preventing it from leaving the cell during the decolorization step. This is what allows gram-positive cells to retain the purple color while gram-negative cells are counterstained with safranin. None of the other choices accurately describe the purpose of a mordant in the Gram stain.

Question 2

This microscope produces an image of a light cell against a dark background; internal structures are NOT visible.

Accepted Answer

A darkfield microscope produces an image of a light cell against a dark background by directing light at an angle to the specimen, so only the scattered light is visible. Internal structures are not visible in darkfield microscopy.

Question 3

In using this microscope, the observer does NOT look directly at an image through a lens.

Accepted Answer

E

Question 4

Which of the following is NOT true regarding the acid-fast stain?

Accepted Answer

If cells are acid-fast, it does not indicate their gram status. Gram status is determined by the presence of a thick peptidoglycan layer in the cell wall, which is not related to acid-fastness.

Question 5

Simple staining is often necessary to improve contrast in which microscope?

Accepted Answer

Simple staining is a technique used to improve contrast in compound light microscopy.

Question 6

Which of the following places the steps in the correct sequence? 1- Staining
2- Making a smear 3-Fixing

Accepted Answer

The correct sequence of preparing a bacterial smear is making the smear, fixing it, and then staining it. Therefore, the correct sequence is 2-3-1, which corresponds to answer choice D.

Question 7

A virus measures 100 nm in length. What is its length in μm?

Accepted Answer

1 nm = 0.001 μm
Therefore, 100 nm = (100 x 0.001) μm = 0.1 μm.

Question 8

What structure does light pass through after leaving the condenser in a compound light microscope?

Accepted Answer

The answer of What structure does light pass through after...

Question 9

The negative stain is used to

Accepted Answer

The answer of The negative stain is used to
...

Question 10

Which of the following is never useful for observing living cells?

Accepted Answer

The scanning electron microscope is not useful for observing living cells as it requires samples to be fixed and coated with electron-dense material, which causes the cells to die. The other microscopes listed are useful for observing living cells in different ways. The phase-contrast microscope enhances the contrast of transparent specimens, the scanning acoustic microscope detects sound waves reflected off cellular structures, the brightfield microscope illuminates the sample from below for clear visualization, and the darkfield microscope enhances the contrast of light-reflecting parts of the sample.

Question 11

Which of the following correctly traces the path of light through the compound microscope?

Accepted Answer

The correct path of light in a compound microscope is from the light source to the condenser, then the specimen, objective lens, and finally the ocular lens. Option B correctly follows this order.

Question 12

Which microscope uses visible light?

Accepted Answer

The answer of Which microscope uses visible light?
...

Question 13

A microorganism measures 5 μm in length. Its length in mm would be

Accepted Answer

To convert micrometers to millimeters, we need to divide by 1000. Therefore, 5 μm = 5/1000 mm = 0.005 mm.

Question 14

Which of the following places the steps of the Gram stain in the correct order? 1-Alcohol-acetone 2-Crystal violet
3-Safranin 4-Iodine

Accepted Answer

The answer of Which of the following places the steps...

Question 15

Figure 3.1  In Figure 3.1, line ʺcʺ points to the microscopeʹs

Accepted Answer

The answer of Figure 3.1  In Figure 3.1, line...

Question 16

Which of the following pairs is mismatched?

Accepted Answer

Basic dyes are used for positive staining as they bind to acidic components of the cell, such as nucleic acids. Negative stains, on the other hand, use acidic dyes that are repelled by the negatively charged bacterial surface. Therefore, the pairing of basic dye with negative stain is mismatched.

Question 17

Which microscope achieves the highest magnification and greatest resolution?

Accepted Answer

Electron microscopes achieve the highest magnification and greatest resolution due to their use of a beam of electrons instead of light. This allows for the visualization of smaller structures than can be seen with a compound light microscope.

Question 18

Which microscope is used to see internal structures of cells in a natural state?

Accepted Answer

The phase-contrast microscope is used to see internal structures of cells in a natural state by using differences in refractive index to enhance contrast without staining or altering the sample.

Question 19

Which of the following pairs is mismatched?

Accepted Answer

Safranin is a basic dye, not an acid dye.

Question 20

Which of the following is NOT equal to 1 mm?

Accepted Answer

The answer of Which of the following is NOT equal...

Quiz 3: Observing Microorganisms Through a Microscope

The purpose of a mordant in the Gram stain is to

This microscope produces an image of a light cell against a dark background; internal structures are NOT visible.

In using this microscope, the observer does NOT look directly at an image through a lens.

Which of the following is NOT true regarding the acid-fast stain?

Simple staining is often necessary to improve contrast in which microscope?

Which of the following places the steps in the correct sequence? 1- Staining 2- Making a smear 3-Fixing

A virus measures 100 nm in length. What is its length in μm?

What structure does light pass through after leaving the condenser in a compound light microscope?

The negative stain is used to

Which of the following is never useful for observing living cells?

Which of the following correctly traces the path of light through the compound microscope?

Which microscope uses visible light?

A microorganism measures 5 μm in length. Its length in mm would be

Which of the following places the steps of the Gram stain in the correct order? 1-Alcohol-acetone 2-Crystal violet 3-Safranin 4-Iodine

Figure 3.1 In Figure 3.1, line ʺcʺ points to the microscopeʹs

Which of the following pairs is mismatched?

Which microscope achieves the highest magnification and greatest resolution?

Which microscope is used to see internal structures of cells in a natural state?

Which of the following pairs is mismatched?

Which of the following is NOT equal to 1 mm?