American Society for Clinical Pathology (ASCP) Histotechnologist Practice Test

What type of microscope is best for examining unstained living cells?

1. Bright-field microscope

2. Fluorescence microscope

3. Phase-contrast microscope

4. Electron microscope

The correct answer is: Phase-contrast microscope

Phase-contrast microscopes are specifically designed to enhance the contrast of transparent and colorless specimens, such as living cells, without the need for staining. This type of microscopy exploits differences in the refractive index of cellular components, allowing for the visualization of structures that would otherwise be nearly invisible under standard bright-field microscopy. By converting phase shifts in light passing through the specimen into amplitude changes, phase-contrast microscopy makes details of the cell's internal structures more apparent. Because living cells are often too transparent to be adequately observed with conventional bright-field techniques, using phase contrast significantly improves visualization, making it easier to study cellular dynamics in real time. While other types of microscopes, like fluorescence and electron microscopes, are powerful, they may not be suitable for directly observing living, unstained cells. Fluorescence microscopy requires fluorescent dyes or tags, and electron microscopy necessitates extensive sample preparation that usually involves fixation and dehydration, which kills the cells and alters their natural state. Thus, phase-contrast microscopy is the preferred method for examining unstained living cells due to its ability to visualize cellular details without altering the specimen.