To observe the endoplasmic reticulum in a cell, which instrument would be used?

• A. Light microscope
• B. Confocal microscope
• C. Transmission electron microscope
• D. Electron microscope

Answer: (D)

The ability to observe the endoplasmic reticulum relies on imaging with much higher resolution than light can provide. The ER is a network of membranes inside the cell, and its details are smaller than the limit at which light microscopes can clearly distinguish structures. Light microscopes are limited by the wavelength of visible light, giving a resolving power of about 200 nanometers, which is not enough to reveal the ER’s membrane-bound network in detail.

Electron microscopes use beams of electrons, which have much shorter wavelengths, giving nanometer-scale resolution. This allows you to see membranes and the intricate network of the ER inside the cell. Among electron microscopes, the transmission electron microscope is especially suited for viewing internal ultrastructure, since it transmits electrons through thin sections of specimen to reveal internal details; scanning electron microscopes reveal surfaces more than interiors.

So, an electron microscope is used to observe the endoplasmic reticulum, with transmission electron microscopy being the typical choice for internal organelle structure.