Sunday, June 8, 2008

Cells: Online Lab #1

Although the use of tools to magnify objects appears to date back to Egyptian times,credit for the first compound microscope is generally given to Zacharias Janssen (source1). This invention was a significant one for the field of science. It opened up a whole new world to the scientists of the time. The microscope's importance to the field of biology continues today. Robert Hooke is another notable scientist who's interest in everythings science drove him to develop the iris diaphragm along with one of the best compound microscope and illumination systems of his time (source4). He is also well known for his book Micrographia in which he provdes a detailed record of his observations of organisms that he viewed under his microscope (source4). Another man of note is Anton van Leeuwenhoek who is discovered, among other things, bacteria, free-living and parasitic microscopic protists, sperm cells, blood cells, and much more (source5). He is also well-known for his skill in producing less complicated, but highly powerful for the time, single lens microscopes (source5).

For students new to biology, one of the most important set of skills to learn is how to use and care for a compound light microscope. The purpose of this lab is to gain these skills.

But before learning how to use the microscope, one should also understand how it works. This can be explained by going through the functions of just a few of the parts of the microscope. The condenser is a lens systems that focuses and aligns light from the light source onto the specimen (source2). The light transmits the image through the objective lens which brings the image of the specimen into focus (source3). The image is then further magnified as it passes through a second set of lenses called the ocular lenses (source3).

Now onto the lab. As instructed, I viewed the video presentation, completed the tutorial, and viewed the 4 slides. After doing so, below is my understanding of how the parts of a microscope work.

1. Stage - The stage is the platform onto which the slide is placed. It holds the slide/specimen level. The stage is adjusted by turning either the coarse adjustment knob or the fine adjustment knob. I only adjust the stage height using the coarse adjustment knob when looking at the microscope.
2. Focus knobs
a. Coarse adjustment knob - The coarse adjustment knob is used to bring the specimen into the focal plane of the objective lens (source2). The coarse adjustment knob is adjusted by turning the top either away from yourself (to raise the stage) and towards yourself (to lower the stage). The coarse adjustment knob should only be used while looking at the microscope.
b. Fine adjustment knob - The fine adjustment knob is used to bring the image into focus. The fine fine adjustment knob is adjusted by turning the knob. Turning the knob raises and lowers the stage in very small increments. The fine adjustment knob can be used while looking through the microscope.
3. Iris - The iris controls the amount of light that is projected from the light sourse onto the specimen. The amount of light that passes through the iris is adjusted by moving the lever located under the stage from sided to side. Depending on the model, the microscope may have a diaphragm instead of an iris. The diaphragm has pre-drilled holes in a metal plate that also vary the amount of light that reaches the specimen. The amount of light passing through the iris can be adjusted while looking through the microscope, but caution should be taken. A minimum amount of light should be let through initially to protect the eyes from bright light.
4. Oculars - The oculars are the part of the microscope that you look through. They contain lenses that further magnify the image transmitted from the objective lens. The distance that the oculars are from each other are ajusted by sliding one of the oculars towards or away from the other. They should be adjusted until the the two circles of light line up to form only 1 circle. The distance of the oculars should be adjusted while looking through the microscope.
5. Objectives - The objective lens gathers light from the specimen and magnifies the image. There are ususally at 3 objective lenses on a compound light microscope that each provide different levels of magnification. When viewing a specimen, you should always start with the lowest magnification and move up to the highest, centering and focusing the image as you move along. You move from one objective to the next by turning the nosepiece. The objectives should be changed when looking at the microscope.

I chose the cheek smear as the image to post here. You can clearly see one complete cell just north of the centerline. I believe you can see the darker line of the plasma membrance encircling the cell along with the dark spot that is the nucleus. There are about 7 other cells (complete and/or partial parts) that you can see in this image. (You can click on the image to get a larger view.)

This lab was a great introduction to the microscope, and the simulator was amazingly like using a real microscope. Through the readings I was able to get a good grasp of the correct techniques that should be used when handling, using, and storing a microscope in order to protect it for future use. The websites provided along with a few others provided great resources to learn about the parts of the microscope, what the function of each is and how to correctly use each one. Most importantly though, I have found myself fascinated by what things look like at the cellular level and want to view things under a real microscope! I was also fascinated by the images I came across as seen through a scanning electron microscope.

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