The transmission electron microscope is most useful for
looking at surface details of a virus
viewing a cell's mitochondria
seeing animal tissue that is visible to the naked eye
studying the structures of a live paramecium

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Viewing a cell's mitochondria.  

A transmission electron microscopy is a microscopic technique in which a beam of electron is transmitted through a specimen to form an image. It magnifies the structure of the specimen with high resolution as compared to light microscopes. It can be used to examine the internal structure of the cell. Transmission electron microscopy can be used to study the organelles in the cells. Hence, it can be used to view a cell's mitochondria.

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