What do scanning electron microscopes and transmission electron microscopes have in common? both generate three-dimensional images. both offer magnification to the atomic level. both are used to view the parts of a cell. both require a vacuum.

Both require a vacuum.

The transmission electron microscope and scanning electron microscopes are two microscopic techniques which uses a high speed and energy electron beams to create an image of the specimen. Scanning electron microscopy creates the image of the specimen by detecting reflected electrons from specimen whereas transmission electron microscopy involves transmission of electrons by the specimen. Both scanning and transmission electron microscopes require vacuum. The flow of electrons is facilitated by a chamber maintained at high vacuum. The vacuum increases the speed and energy of electrons interacting with the specimen.

when it is at an intermediate population density

links? do you have a link? i don't see anything?