Microscopes are important to visualize cells. The small size of cells makes the use of microscopes necessary; if two objects are close together; they start to look like one object. But if we can distinguish them, then it is said that we’ve resolved them. With normal human vision, the smallest objects that can be resolved is about 200 um (.2 mm in size).

The two most common types of microscopes are light microscopes and electron microscopes.

Light microscopes use light as a source of radiation and have a resolving power of .2 um (200 nm). This is one thousand times better than that of the human eye.

Electron microscopes, on the other hand, use electrons as a source of radiation instead of light. They also have magnets instead of glass lenses to focus an electron beam. The wave-length of an electron beam is far shorter than that of light. And the resulting image resolution is far greater. Also, a fluorescent screen resolution is .5 nm or 400 thousand times better than the human eye. However, in electron microscopes, cells have to be put in a vacuum in order to avoid the molecules in the cell to interact with the other gases in the atmosphere. The problem with this is that water boils in a vacuum at room temperature. Therefore, the cell needs to be dehydrated and killed. In addition, the components of the cell are colorless and need to be stained in order to view them.

Complicated right?

Also, there are two popular types of electron microscopes (EM) that provide different points of view of the cell; Scanning EM which provides a 3-dimensional view of the cell surface or topography and Transmission EM which provides an inside access into the components of a cell and it’s molecules.

I understand this is a short post but a very relevant one. This is all there is to the introduction, next post we’ll discuss the molecules of a cell.