Which electron microscope primarily studies the internal ultrastructure of cells?

The Transmission Electron Microscope (TEM) is specifically designed to study the internal ultrastructure of cells. This type of microscope works by transmitting a beam of electrons through a thinly sliced specimen. As the electrons pass through the sample, they interact with the cellular structures, allowing for high-resolution imaging of internal components such as organelles and membranes. The ability of the TEM to achieve greater magnifications and resolutions than other microscopes, such as light microscopes, is due to the shorter wavelength of electrons compared to visible light.

In contrast, a Scanning Electron Microscope (SEM) provides detailed three-dimensional images of the surface of specimens rather than their internal structures. A Standard light microscope is limited in resolution and cannot provide the level of detail necessary for examining internal cell ultrastructure. Fluorescence microscopes are primarily used to visualize specific cellular components that are labeled with fluorescent dyes, offering insights into molecular distributions but not detailed internal ultrastructure. Therefore, the TEM is the optimal choice for studying the intricate internal details of cells.