Microscopes and Cells
Students explore the microscopic world using microscopes.
The human eye see cannot objects smaller than 0.1mm. To see objects small we must magnify or enlarge them. Using the dots below, look at A through F. You will notice that A has a specific weave, while F looks solid. What is happening is that each iteration is zoomed out slightly, making a weaved object look more solid the more you zoom out.
History of the Microscope
Microscopes work on the principle of refracting light through a lens, or magnification. One of the first scientists to explore the microscope was Anton van Leeuwenhock (1632-1723). He was a Dutch linen merchant that had a talent for grinding small glass lenses. Using this talent, he constructed an instrument called the microscope that could magnify objects up to 300 times (300x). Using these tools he was the first person to observe single celled organisms, which he called “animalcules.”
About the same time that Leeuwenhoek was making his observations in Holland, the English scientist Robert Hooke (1635–1703) was experimenting with microscopes he had built, like the one in Figure 2.3. Hooke looked through his microscope at a thin piece of cork that he had cut from the bark of an oak tree. He saw a network of tiny box-like compartments that reminded him of a honeycomb. He described these little boxes as cellulae, meaning “little rooms” in Latin. Hooke’s descriptions have given us our present-day word “cell.”
Over the next century, many other scientists used microscopes to study microorganisms and to look at different parts of plants and animals. They saw cells in every living thing they examined. In 1839 German botanist Matthias Schleiden and zoologist Theodore Schwann combined their observations. They made the hypothesis that all organisms are composed of cells. A cell is the basic unit of life, they suggested, because all the functions eyepiece carried out by living things are carried out by their individual cells, as well. German scientist Rudolf Virchow contributed his ideas to those of Schleiden and Schwann. Their ideas tube formed the basis for a set of hypotheses called the cell theory. Two important points of this theory that you will learn about are:Science Focus 8, pp. 103-104
With advancements in technology, new microscopes today can magnify objects as much as 2000x. However, this is still not enough to observe the smaller structures of a cell and other minut objects. To see smaller objects, scientists use electron microscopes, which uses beams of electrons instead of light. These electronics bounce off the object, forming an image on a screen to be viewed. Today’s electron microscopes can magnify objects up to 2 000 000x times.
Parts of a Optical (Light) Microscope
Using a Microscope
Use the following steps when operating a microscope.
- Position the microscope at your work area with the arm toward you. If the microscope has an electric cord for the light source, make sure the cord is properly connected and plugged in.
- Use lens paper to clean the lenses and the lightsource (or mirror). Do not touch the lenses with your fingers.
- The microscope should always be left with the low-power objective lens in position. If it is not, rotate the revolving nosepiece until the low-power objective lens clicks into place.
- Looking from the side, use the coarse-adjustment knob to lower the objective lens until it is about 1 cm above the stage.
- Look through the eyepiece (ocular lens) and adjust the diaphragm until the view is as bright as you can get it.
- Place a prepared slide on the stage. Make sure the sample (object to be viewed) is centred over the opening.
- Look through the eyepiece and slowly turn the coarse-adjustment knob until the sample is in focus.
- Use the fine-adjustment knob to sharpen the focus.
- To see more details, rotate the revolving nosepiece to the next objective lens. Do not change the focus first. After the medium-power objective lens has clicked into place, adjust the focus using only the fine adjustment knob. Do not use the coarse-adjustment knob with high and medium powered lenses.
- Sketch your sample.
Calculating the Field of View
Field of view refers to the space that is visible when viewing through the microscope. You can calculate the field of view if you know the diameter of the low-power lens. Use the formula below to help calculate the field of view.
If, for example, your low-power objective lens is a 4× lens with a field of view of 4 mm, and your medium-power objective lens is a 10× lens, then your calculations would be: