An electron microscope uses a beam of electrons instead of light. Electrons have a much shorter wavelength than light, so the resolution is far higher: an electron microscope can resolve objects well under 1 nm apart, compared with about 200 nm for a light microscope. Magnifications of more than ×500 000 are possible, which shows the ultrastructure of cells, such as membranes, ribosomes and the inner structure of mitochondria.Electrons cannot be focused by glass, so electromagnets act as the lenses. The image is formed on a fluorescent screen or detector and recorded as an electron micrograph. Micrographs are black and white; any colour is added afterwards by computer (false colour).The whole column must be kept under a vacuum, because air molecules would scatter the electrons. This means specimens must be dead and dehydrated.Limitations
• Living cells cannot be viewed, so movement and processes cannot be watched.
• Specimen preparation is long and complex (fixing, dehydrating, staining with heavy metals, cutting or coating).
• Preparation can create artefacts, structures that were not present in the living cell, so results must be interpreted carefully.
• The microscopes are very large and expensive, and need trained operators.There are two main types: the transmission electron microscope (TEM), which sends electrons through a thin section, and the scanning electron microscope (SEM), which scans electrons across the surface of a specimen.
• Living cells cannot be viewed, so movement and processes cannot be watched.
• Specimen preparation is long and complex (fixing, dehydrating, staining with heavy metals, cutting or coating).
• Preparation can create artefacts, structures that were not present in the living cell, so results must be interpreted carefully.
• The microscopes are very large and expensive, and need trained operators.There are two main types: the transmission electron microscope (TEM), which sends electrons through a thin section, and the scanning electron microscope (SEM), which scans electrons across the surface of a specimen.