Final answer:
Phase-contrast microscopes are ideal for observing live specimens, utilizing light phase shifts and refractive index differences to create high-contrast images without staining, revealing details in eukaryotic and prokaryotic cells.
Step-by-step explanation:
Phase-contrast microscopes are particularly useful for viewing live specimens because they enhance the contrast of transparent and colorless structures without the need for stains. This type of microscopy takes advantage of differences in the refractive indices of cellular components, like eukaryotic organelles and prokaryotic endospores. Phase-contrast microscopy involves shifting the phase of light waves by half a wavelength to capture these differences and produce a clear image with high contrast. It utilizes a phase plate to cause destructive interference, where wave peaks and troughs cancel each other out, making structures that refract light appear dark against a bright background. Thus, these microscopes are especially effective in revealing details within live, unstained specimens, offering a three-dimensional appearance to the observed structures.