1. Simple optical microscope. One lens. Disadvantage: Only Van Leeuwenhoek made them, and he's dead. Advantage: Worked pretty well. With them, Van Leeuwenhoek discovered protozoa and bacteria.
2. Compound optical microscope. Has both an ocular and objective lens. Disadvantage: limited resolution. Can resolve bacteria, but not smaller things like viruses. Advantage: can be used with live specimens (using phase contrast or polarized or other special illumination).
3. Binocular dissecting microscope (optic). Has a pair of ocular and objective lenses, and supposedly presents a "3D" view of the specimen to the viewer (I was never able to see in 3D using these darn things). Disadvantage: Limited magnification Advantage: Can be used to perform surgery on small but not microscopic specimens, such as fruit flies. Is used in "microsurgery" in hospitals too.
The three types of specimens a dissecting microscope are as follows:
Optical Microscopes.
Electron Microscopes.
Scanning Probe Microscopes.
Optical microscopes are the oldest and the simplest microscope it uses a single convex lens to enlarges the image placed under its focus.
Electron Microscope is used by scientists to study cell, this microscope fire beams of electrons on the subject which is held in the vacuum-sealed tubes.
Scanning probe microscopy is a powerful microscope, it can detect matters smaller than the nano-meter however its images have no color because it uses probe measure things other than visible light.
The human genome density ranges between 12-15 genes per Megabase pairs. This is because humans have approximately 2000 genes in a total of approximately 3 billion base pairs. However, some primitive organisms have an even larger gene density
than humans. An example is bacteria with gene densities ranging between 100 –
500 genes/Mb. Gene density is therefore
not a good characteristic in determining
the complexity of an organism.
