Which electron microscopy requires ultrathin sectioning and osmium tetroxide staining?
Transmission Electron Microscopy images internal ultrastructure by passing electrons through ultrathin sections typically 50-100 nm. Biological material lacks contrast, so fixation with osmium tetroxide, which binds lipids and adds electron density, plus dehydration, resin embedding, and staining with heavy metals like lead citrate is required. Ultramicrotomy produces sections thin enough for electron transmission. Unlike SEM which shows surface, or AFM which probes topography, TEM reveals organelle membranes, ribosomes, and viral capsids at ~0.2 nm resolution, but demands extensive sample preparation.
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.