To observe the endoplasmic reticulum in a cell, which instrument would you use

• A. Light microscope
• B. Ultracentrifuge
• C. Electron microscope
• D. Dissecting instruments

Answer: (C)

Seeing the endoplasmic reticulum requires imaging with very high resolution because it is a network of membrane-bound tubules and sacs packed within the cytoplasm. Light microscopes rely on visible light and have limited resolving power (about 200 nanometers), which isn’t enough to clearly distinguish the ER’s thin membranes and the fine details of its interior. Electron microscopes use beams of electrons with much shorter wavelengths, giving nanometer-scale resolution, which lets you visualize the membrane layers and the interconnected network of the ER. In practice, transmission electron microscopy is commonly used to view internal cellular ultrastructure like the ER, while scanning electron microscopy shows surface features. The other options aren’t imaging tools: an ultracentrifuge separates cell components by density, and dissecting instruments are for physical manipulation, not for observing internal structures.