Biology 156: Online Microscope Lab

Today, microscopes are an important part of everyday life whether it is basic use in schools looking at cheek cell and onion roots, or advanced use in the different fields of science to image single layer crystals of DNA transcription enzymes.

The first microscope is thought to have been created by the Janssen's

around 1595. This microscope was a tube with two lenses, one at each end. Robert Hooke would later improve on the compound microscope and would also come up with the word "cell" to describe features of plant tissue that he was able to see with the use of a microscope. Anton van Leeuwenhoek built the best microscopes of his time period (1632-1723) and was the first person to describe bacteria and protozoans. He also helped prove the theory of blood circulation. All of these founding fathers helped to contribute to the modern day microscope.

One of the most common microscopes used today is the compound microscope.

The stage of a microscope is the platform that supports the specimen. It is perpendicular to the optical axis and completely flat. The stage is adjusted using the course adjustment knob, and should be adjusted while looking at the microscope.

There are two different focus knobs on this microscope: the course adjustment and the fine adjustment. The course adjustment knob moves the body tube or the stage up and down by a rack and pinion assembly. This adjustment should initially be done while looking at the microscope. Then you can look through the microscope and move the course adjustment down slowly until your specimen is visible. The course knob should not be adjusted at hight resolutions. The fine focus knob is for precise focusing of your specimen and is used more frequently than the course focus. The fine focus should be adjusted while looking through the microscope.

The iris serves to control the angle of the cone of light emerging from the top of the conderser. This can be adjusted to control contrast and should be adjusted while looking through the microscope.

The ocular is the eyepiece. The optics in the microscope magnify what is called the "virtual image" that is formed by the objective. The ocular converts this into what is called a "real image" that can be seen directly by the eye. An ocular cannot improve the inherit resolution of the image. Some microscopes have two oculars. These can be adjusted by turning the microscope on, starting at a setting of 64, and then looking through the microscope and adjusting the distance between the occulars until the 2 circles of light become one.

The objectives are the magnifiying part of the microscope and are attatched to the rotating nose piece. The most common are 4x, 10x, 40x and 100x. These should be rotated while looking at the microscope.

In the online lab, I looked at an onion root tip at 40x as seen below

Without the microscope, many discoveries and advances in biology as we know it would not have been possible. Until the microscope was invented in the early 1600's, cells could not be seen or for that matter, even imagined. With the use of microscopes, new single celled organisms appeared that did not fall into the current two-kingdom classification system that was being used at the time. The great diversity of these organisms prompted the creation of a third kingdom which included bacteria. The invention of the microscope also led to the development of microscopic anatomy consisting of histology, and cytology. Advances in the microscope have opened up unexplored fields of anatomical investigations, and today cell biology has merged with genetics and molecular biology and created a unified science of life. We continue to make advances in the fields of biology and medicine that would not be possible if that first microscope wasn't invented back in 1595.