The cell structure that cannot be seen with light microscopy is ribosomes.

Here's why:

* Size: Ribosomes are incredibly small, measuring only about 20-30 nanometers in diameter. This is significantly smaller than the resolution limit of light microscopes, which is around 200 nanometers.

* Light Microscopy Limitations: Light microscopes use visible light to illuminate and magnify objects. The wavelength of light limits the smallest detail they can resolve.

To visualize ribosomes, we need more powerful techniques like:

* Electron microscopy (EM): EM uses electrons instead of light, providing much higher resolution and allowing for the visualization of tiny structures like ribosomes.

Let me know if you have any other questions!