27. From the following statements:
A. Coloured images can be obtained by transmission electron microscopy by fluorescent labelling of the specimen
B. Scanning electron microscopy requires sectioning of the sample
C. Confocal microscopy uses optical methods to obtain images from a specific focal plane and excludes light from other planes
D. Differential-interference microscopy relies on interference between polarized light due to differences in the refractive index of the object and surrounding medium
E. Visualization in epifluorescence microscopy requires staining by heavy metal atoms
Choose the combination with two correct and one incorrect statements.
A. B, C, E
B. A, B, E
C. A, C, D
D. B, D, E
Confocal microscopy (C) and DIC (D) are correct; A, B, and E are incorrect microscopy principles.
Correct Answer
C. A, C, D (two correct: C+D; one incorrect: A)
Statement Analysis
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A. TEM colored images fluorescent labelling: INCORRECT. TEM produces grayscale electron density images; fluorescence is light microscopy only.
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B. SEM requires sectioning: INCORRECT. SEM images surfaces directly; sectioning is TEM requirement.
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C. Confocal optical sectioning: CORRECT. Pinhole excludes out-of-focus light for z-resolution.
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D. DIC polarized interference: CORRECT. Refractive index gradients create 3D-like contrast.
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E. Epifluorescence heavy metal staining: INCORRECT. Uses organic fluorophores; heavy metals for EM.
Option Breakdown
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A. B,C,E: 1 correct (C) → Wrong
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B. A,B,E: 0 correct → Wrong
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C. A,C,D: 2 correct (C,D) + 1 wrong (A) → CORRECT
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D. B,D,E: 1 correct (D) → Wrong
Confocal microscopy optical sectioning eliminates out-of-focus blur via pinhole aperture, essential for 3D organelle imaging in thick specimens.
Statement Verification Table
| Statement |
Technique |
Correct? |
Principle |
| A |
TEM fluorescent |
❌ False |
Grayscale electron contrast |
| B |
SEM sectioning |
❌ False |
Surface imaging only |
| C |
Confocal pinhole |
✅ True |
Z-resolution |
| D |
DIC interference |
✅ True |
Refractive index |
| E |
Epifluorescence heavy metal |
❌ False |
Organic fluorophores |
Answer C: C+D correct, A wrong. Classic GATE pattern testing technique fundamentals.
Core Principles Memory Aid
TEM: Transmission → Thin sections → Grayscale
SEM: Surface → No sectioning → 3D topography
Confocal: Pinhole → Optical sectioning → Z-stack
DIC: Polarized → Refractive index → Pseudo-3D
Epifluorescence: Fluorophores → Excitation/Emission → Live cells
Exam Strategy: Confocal/DIC always correct for optical principles; EM statements usually test sectioning vs surface differences.
