Histology Certification Microscopy Techniques 2 — Questions and Answers
Question 1: What is the primary advantage of phase contrast microscopy over bright-field microscopy when viewing unstained cells?
- It provides color differentiation
- It converts phase differences into amplitude differences, enhancing contrast (Correct answer)
- It increases the magnification limit
- It eliminates the need for a condenser
Correct answer: It converts phase differences into amplitude differences, enhancing contrast
Phase contrast microscopy converts subtle differences in refractive index into visible contrast differences, allowing unstained living cells to be visualized clearly.
Question 2: In confocal laser scanning microscopy, what is the purpose of the pinhole aperture?
- To increase the intensity of the laser beam
- To exclude out-of-focus light and improve axial resolution (Correct answer)
- To split the laser beam into multiple channels
- To convert laser light into white light
Correct answer: To exclude out-of-focus light and improve axial resolution
The pinhole aperture in confocal microscopy blocks out-of-focus fluorescent light, enabling optical sectioning and high-resolution 3D reconstruction.
Question 3: Which type of objective lens provides the highest numerical aperture and requires immersion oil?
- 4x dry objective
- 10x plan achromat
- 40x water immersion
- 100x oil immersion (Correct answer)
Correct answer: 100x oil immersion
The 100x oil immersion objective achieves numerical apertures up to 1.4 by using immersion oil that matches the refractive index of glass, maximizing light collection.
Question 4: What does the term 'parfocal' mean in the context of microscope objectives?
- All objectives have the same magnification
- Objectives remain approximately in focus when switching between them (Correct answer)
- All objectives produce the same field of view
- Objectives are corrected for chromatic aberration
Correct answer: Objectives remain approximately in focus when switching between them
Parfocal objectives require only minor refocusing when switching magnifications because they are designed to maintain approximately the same focal plane.
Question 5: In transmission electron microscopy (TEM), what is the function of the objective aperture?
- To accelerate electrons toward the specimen
- To improve contrast by blocking scattered electrons (Correct answer)
- To magnify the image onto the detector
- To produce the electron beam
Correct answer: To improve contrast by blocking scattered electrons
The objective aperture in TEM blocks highly scattered electrons, improving image contrast by allowing only minimally scattered electrons to contribute to the final image.
Question 6: Which microscopy technique is best suited for imaging surface topography of a specimen at nanometer resolution?
- Wide-field fluorescence microscopy
- Scanning electron microscopy (SEM) (Correct answer)
- Bright-field light microscopy
- Phase contrast microscopy
Correct answer: Scanning electron microscopy (SEM)
SEM generates detailed three-dimensional surface images by detecting secondary electrons emitted from the specimen surface, providing nanometer-scale topographical resolution.
Question 7: What is the Rayleigh criterion for the limit of resolution in optical microscopy?
- d = λ / (2 NA)
- d = 0.61λ / NA (Correct answer)
- d = λ × NA
- d = 2λ / NA
Correct answer: d = 0.61λ / NA
The Rayleigh criterion states that the minimum resolvable distance is d = 0.61λ/NA, where λ is the wavelength of light and NA is the numerical aperture.
Histology Certification Microscopy Techniques 2
What is the primary advantage of phase contrast microscopy over bright-field microscopy when viewing unstained cells?