Which microscopy reveals internal structure using transmitted electrons?
Transmission Electron Microscopy reveals internal architecture because accelerated electrons are transmitted through ultrathin specimen. Dense regions absorb or scatter electrons more, creating contrast on screen. Electrons that pass through are focused by electromagnetic lenses to form magnified image of organelles, crystals, and macromolecular complexes. In contrast, SEM detects secondary electrons reflected from surface for topography, while AFM or DIC use probes or interference for surface relief. TEM's transmission geometry enables sub-nanometer resolution of mitochondrial cristae, nuclear pores, and viral interiors after heavy metal staining and sectioning.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.