All organisms are made of cells, the organism's basic unit of structure and function. The microscope's invention and improvement in the seventeenth century led to the discovery and study of cells. In 1665, Robert Hooke described cells using a light microscope. Visible light is focused on a specimen. Light passing through the specimen is refracted with an objective lens and an ocular lens.
Light microscope Two important concepts in microscopy are magnification and resolving power.
Resolution of a light microscope is limited by the wavelength of visible light. Highest magnification in a light microscope with maximum resolution is about 1000 times. Electron microscope . Instead of light, electron microscopes use electron beams which have much shorter wavelengths than visible light. Modern electron microscopes have a practical resolving power of about 2 nm.