10.
The kind of microscope in which image is formed by passing an electron beam through a specimen
and focusing the scattered electrons is
- (A) Transmission electron microscope
- (B) Scanning electron microscope
- (C) Phase-contrast microscope
- (D) Fluorescence microscope
Correct Answer: A. Transmission electron microscope
Transmission electron microscopes (TEM) form images by passing an electron beam through an ultrathin specimen, where electrons are transmitted or scattered based on specimen density, creating contrast for high-resolution internal imaging.
Option Analysis
A. Transmission Electron Microscope
TEM uses a high-energy electron beam passed through electron-transparent specimens (≤100 nm thick), focusing transmitted and scattered electrons to form 2D projection images of internal ultrastructure. This matches the description perfectly, enabling atomic-level resolution (~0.1 nm).
B. Scanning Electron Microscope
SEM scans a focused electron beam across a surface, detecting emitted secondary or backscattered electrons from interactions at the surface, not transmitted through the specimen. It provides 3D topography, not internal transmission imaging.
C. Phase-Contrast Microscope
Phase-contrast uses visible light passed through living cells, exploiting phase shifts in refracted light (not scattered electrons) to enhance contrast in transparent specimens without staining. No electron beam is involved.
D. Fluorescence Microscope
Fluorescence excites fluorophore-labeled molecules with light, imaging emitted longer-wavelength light, not electrons passed through specimens. It reveals molecular localization, not electron transmission.
Introduction to Microscope Electron Beam Through Specimen
The microscope electron beam through specimen technique defines transmission electron microscopy (TEM), essential for visualizing cellular ultrastructure in biology and GATE Life Sciences exams.
How TEM Works
Electrons accelerate through a vacuum column, pass through ultrathin sections on grids, and interact via elastic/inelastic scattering to form bright-field/dark-field images. Magnetic lenses focus the beam like light optics but with ~100,000x shorter wavelength.
Technique Comparison Table
Microscope Type Beam Type Image Formation Resolution Best For TEM Electrons through specimen Transmitted/scattered electrons 0.1 nm Internal ultrastructure SEM Electrons on surface Emitted secondary electrons 1 nm Surface topography Phase-Contrast Visible light Phase shifts 200 nm Live cell contrast Fluorescence Light Emitted fluorescence 200 nm Molecular labeling GATE Life Sciences Exam Tips
For microscope electron beam through specimen questions, distinguish TEM (transmission) from SEM (surface scanning)—TEM requires thin sections. Review PYQs on resolution limits.
Research Applications
TEM reveals viruses, organelles, and protein complexes, often combined with immuno-gold labeling for specific protein localization. Cryo-TEM advances structural biology.
