2nd Summary: Microscopy and Photomicrography January 26, 2014 Dr. Robert Ross

Scientists, in this case biologists, use microscopes, an optical instrument that uses lenses to produce

magnified images of cells and explore their internal mechanisms. There are different types of

microscopes with different functions such as the light microscope (LM), in which visible light passes

through the specimen. Examples of LM include brightfield, mostly used for identification of cells usually

by gram staining, which was the one used to view Saccharomyces cerevisiae. The organism was placed

in a water-filled tube which then half of the solution was poured into a new tube that also contained

water and so on. The purpose of this technique is to dilute the organism so that the concentration of the

solute is decrease, in this case Saccharomyces, and the amount of solute per volume unit of the solvent

decreases. This technique allows yeast to separate and the space between each organism to become

larger, which can then be watched through the microscope more clearly. The organisms viewed through

the microscope were not completely separated, which could have been resolved by performing more

dilutions so that the spaces between each yeast would be greater.Dark-field microscopy is used for living

organisms that cannot be stained and are invisible through a LM. Living unpigmented cells are

distinguished from their organelles due to their tendency to bend light by using phase contrast. When

living specimens do not possess optical contrast in bright-field, Nomarski is used. Instead of light, the

electron microscope (EM) focuses a beam of electrons through the specimen. Two types of EM are

scanning electron microscope (SEM), which focuses on the sample’s surface and composition, and

transmission electron microscope (TEM), in which the internal structures can be distinguished.

Microscopes allow scientist to view things from a molecular perspective for a better understanding of

how life works.