Question 1

Which of the following best describes the concept of resolving power in microscopy?

Accepted Answer

The ability of a microscope to distinguish two adjacent points as separate entities.

Question 2

The resolution ($$R) of a $$light microscope objective lens is given by the formula $$R = \frac{0.61 \lambda}{n \sin 	heta}. $$What does $$n \sin 	heta$$ represent in this equation?

Accepted Answer

The numerical aperture of the objective lens.

Question 3

Why does using immersion oil between the specimen and the objective lens improve resolution in light microscopy?

Accepted Answer

Immersion oil increases the refractive index ($$n$$), thereby increasing the numerical aperture ($$n \sin 	heta).$$

Question 4

Which of the following is a major advantage of transmission electron microscopy (TEM) over standard light microscopy?

Accepted Answer

TEM provides much higher resolution due to the shorter wavelength of electrons.

Question 5

A specimen is prepared for TEM by introducing electron-dense elements. Which of the following is NOT commonly used for this purpose?

Accepted Answer

Sodium

Question 6

In fluorescence microscopy, what is the role of the dichroic mirror?

Accepted Answer

It selectively reflects excitation light and transmits emitted fluorescence.

Question 7

Which microscopy technique allows for optical sectioning and the creation of three-dimensional reconstructions of specimens?

Accepted Answer

Confocal fluorescence microscopy

Question 8

A student observes a specimen using phase-contrast microscopy. What is the main principle behind the increased contrast in this technique?

Accepted Answer

Phase-contrast microscopy converts phase shifts in light passing through the specimen into differences in intensity.

Question 9

Which of the following best explains why high-aperture lenses provide better resolution in light microscopy?

Accepted Answer

High-aperture lenses collect light over a wider angle, increasing the numerical aperture.

Question 10

A researcher uses indirect immunofluorescence to label tubulin in dividing cells. What is the advantage of using secondary antibodies conjugated to a fluorochrome?

Accepted Answer

Secondary antibodies amplify the fluorescent signal by binding to multiple primary antibodies.

Question 11

Which of the following sample preparation steps is unique to freeze-fracture electron microscopy?

Accepted Answer

Fracturing the specimen along lines of weakness, often through lipid bilayers

Question 12

A scientist wants to visualize the surface topology of a pollen grain. Which microscopy technique should they use?

Accepted Answer

Scanning electron microscopy (SEM)

Question 13

Which of the following statements about confocal microscopy is TRUE?

Accepted Answer

Confocal microscopy uses a pinhole to eliminate out-of-focus light, improving image clarity.

Question 14

A cell biologist is studying actin filaments using a fluorescently labeled phalloidin. What property of phalloidin makes it useful for this application?

Accepted Answer

Phalloidin binds specifically to actin filaments, allowing for their visualization.

Question 15

Which of the following is a limitation of standard bright-field microscopy when observing unstained biological specimens?

Accepted Answer

It provides poor contrast for transparent specimens, making internal structures difficult to see.

Question 16

A student is using a light microscope with a numerical aperture ($$NA) of 1.25 $$and a wavelength ($$\lambda) of 0.63$$ $$\mum. $$What is the theoretical resolution limit ($$R) of $$the objective lens?

Accepted Answer

$$R = \frac{0.61 	imes 0.63}{1.25} = 0.307 \mum$$

Question 17

Which microscopy technique is best suited for visualizing the organization of cytoskeletal filaments in living cells without staining?

Accepted Answer

Phase-contrast microscopy

Question 18

During specimen preparation for TEM, why is glutaraldehyde commonly used?

Accepted Answer

It covalently crosslinks proteins, stabilizing cellular structures.

Question 19

Which of the following best explains the difference between TEM and SEM?

Accepted Answer

TEM transmits electrons through thin sections, while SEM scans the surface with electrons.

Question 20

A researcher wants to visualize the distribution of a specific protein within a cell using fluorescence microscopy. Which labeling method would provide the highest specificity?

Accepted Answer

Indirect immunofluorescence using primary and secondary antibodies

Principles and Applications of Microscopy in Cell Biology

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