Final answer:
The main drawback of light microscopy is its lower resolving power compared to electron microscopy, limiting the ability to see detailed ultrastructures of specimens. Light microscopy also suffers from low contrast when viewing unstained, living organisms, and sample preparation generally requires cells to be fixed and stained.
Step-by-step explanation:
A drawback to using light microscopy is the limited resolving power, which refers to the ability to distinguish between two closely spaced objects. Compared to electron microscopes, light microscopes cannot provide as much detail because they use visible light that has a longer wavelength than electrons. This longer wavelength limits the resolution, making it difficult to view the ultrastructural details of specimens. Additionally, while light microscopes allow for the observation of living cells without killing them, their contrast can be quite low when observing live organisms, making it harder to distinguish the specimen from the background. Enhanced contrast methods like staining can improve visibility but often require the cells to be fixed, which means they are no longer alive.
In light microscopy, samples must be thin enough to allow light to pass through for observation. Specimens also often require staining to increase contrast, unlike in fluorescence microscopy where fluorophores provide contrast. This staining process is a critical difference in sample preparation between fluorescence microscopy and light microscopy. Conversely, electron microscopy requires very thin sections of specimens, and these must typically be dehydrated and coated with metal, a process which ultimately kills the cells.