If a microorganism is 150 nm in size, would it be visible under a standard light microscope?

• A. Yes.
• B. Only with staining.
• C. Only with electron microscopy.
• D. No.

Answer: (D)

Resolution in light microscopy is limited by diffraction and the wavelength of light. Even with good optics, the smallest detail you can resolve with visible light is about 200 nanometers. A microorganism measuring 150 nanometers is smaller than this limit, so it cannot be seen as a distinct object with a standard light microscope. Staining can boost contrast but doesn’t overcome the diffraction limit. To visualize something this small, electron microscopy is needed because electrons have far shorter wavelengths and provide much higher resolution. So, it would not be visible under a standard light microscope; electron microscopy would be required to observe it.