National League for Nursing (NLN PAX) Practice Exam

The electron microscope is the appropriate instrument for observing the endoplasmic reticulum in cells due to its ability to provide significantly higher resolution compared to other types of microscopes. The endoplasmic reticulum, which consists of intricate folded structures and membranes, is typically too small to be seen clearly with a light microscope or even a compound microscope, which utilize visible light for imaging.

In contrast, an electron microscope uses beams of electrons rather than light to create an image and can resolve much finer details, allowing for the clear visualization of cellular structures such as the endoplasmic reticulum, ribosomes, and other organelles at the nanometer scale. This capability makes it the most suitable choice for detailed cellular studies where such small structures need to be analyzed.

Other options, such as stained glass slides, do not apply in this context as they are not instruments for microscopy but rather a method for preparing samples for examination. Thus, the electron microscope stands out as the primary tool for high-resolution imaging of the endoplasmic reticulum within cells.