Aristotle originated the scientific method over 2,000 years ago based on developing reliable knowledge from observation. Islamic and Renaissance polymaths such as Ibn al-Haytham and Galileo Galilei perfected the method to include developing a hypothesis based on observation and devising experiments to confirm, refute or adjust the hypothesis - but observation remains the key first step. In the science of biology, this can sometimes be rather difficult as many organisms and their natural processes are invisible or poorly visualized by the naked eye. As demonstrated in the figure below, our eyes can discern a flea, but not its morphology. Conversely, an optical microscope has no problem establishing its body parts. The main participants of the human reproductive system stand on either side of our ability to see them: we can just make out a human egg with our eyes; but not sperm cells. That takes an optical microscope.
Most cells are smaller than sperm. The typical mammalian cell is on the order of 20 to 30 microns in diameter and is thus completely invisible to the naked eye. Yeast cells and bacteria are about ten times smaller and of about the same dimension as the larger organelles with a cell, such as the nucleus. Smaller organelles, such as mitochondria are of a size close to the limit of an optical microscope's ability to resolve fine structure as defined by the Abbe Limit which dictates that the best resolution you can get is about 200 nm. Yet physicists have found ways to bend the Abbe Limit through super-resolution techniques that drop resolution capabilities of optical microscopes down by about an order of magnitude, such that virus particles can be viewed.
By switching from light rays to streams of electrons, the ability to resolve fine structure in biology can be significantly improved. One can calculate an Abbe Limit for transmission electron microscopy which yields a resolution of about 2Å, sufficient to visualize proteins and protein complexes. Of course the electrons stream only in a vacuum, so don't expect to do any live cell work!
By: BioTek Instruments, Peter Banks Ph.D., Scientific Director