* Ribosomes are incredibly small: They are only about 20-30 nanometers in diameter. This is far smaller than the resolution limit of light microscopes (around 200 nanometers).
* TEM uses electrons: TEMs use a beam of electrons to illuminate the sample. Electrons have a much shorter wavelength than light, allowing for much higher resolution.
* Thin sections: TEM requires samples to be very thin (usually less than 100 nanometers) and often stained with heavy metals to enhance contrast. This allows the electrons to pass through the sample and create an image.
While a scanning electron microscope (SEM) can provide high-resolution images of the surface of cells, it wouldn't be suitable for seeing ribosomes inside the cell because it only shows the external structures.
