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Day 2: Ubiquity of Microorganisms and Microscopy
The term ubiquity means ‘everywhere’, and microorganisms are everywhere. They are in the air, on the ground, in your nose, in your gut, in the hot pools at Yellowstone, at the bottom of the sea, and deep in the bowels of the earth.
Galileo invented the first useful telescope (1609), which could be turned around and used as a crude microscope. He looked at a few insects with his ‘microscope’ but mainly used it to view the heavens and the sun, which eventually led to serious eye damage. Antony van Leeuwenhoek discovered “animalcules” which turned out to be bacteria and protozoa. He observed these organisms everywhere – on his teeth, in his excreta, in his food, in the soil, in pond water. Robert Hooke was the first to report observing cells in thin sections of cork, which comes from the bark of a particular species of oak that grows in Spain. Between microscopic forays, Hooke occupied himself by harassing Sir Isaac Newton, eventually driving Newton to a nervous breakdown.
Parts of Your Microscope – See Figure on page 41 of your textbook
Simple microscopes are comprised of one lens, compound of multiple lenses
Coarse adjustment knob
Fine Adjustment knob
Mechanical stage knobs
Care of Your Microscope
1) Use both hands when carrying the microscope.
2) When focusing on a specimen, always use the lowest power first. Always focus upwards to prevent scratching of lens and breaking of slides.
3) Always wipe immersion oil from lens with an ethanol soaked lens paper (not paper towel or bibulous paper).
Brightfield Microscopy: With this type of microscope, a bright light is directed through the condenser onto the underside of your specimen. Light waves will pass through your specimen into the ocular and then into your eye, showing you the detail within your specimen under magnification. Darkfield Microscopy: Some microorganisms can be seen more easily with a darkfield microscope. This optical tool creates images of microscopic objects by collecting light reflected from the object resting on a dark background. Phase Contrast Microscopy: Sometimes it is necessary to observe structures within your specimen; however, since the cytoplasm of most cells is transparent, a brightfield microscope does not do you justice – instead, a phase-contrast microscope will work better for this mission. This microscope allows half of the light to pass through your specimen and the other half around your specimen. The light passing through specimen is then recombined with light that passed around specimen. Since the light passing through the specimen has slowed down, it is now out of phase with light passing around. The out of phase light interferes with light of the original phase, producing a contrasting image of the sample. Fluorescence Microscopy is a form of darkfield microscopy that detects light emitted from the specimen after it is exposed to ultraviolet, violet or blue light. Fluorescence emission is obtained by tagging the cell or tissue with molecules that fluoresce, or emit light, upon stimulation by electromagnetic radiation . Electron Microscopy is used to provide greater resolution. With Scanning Electron Microscopy the specimen is covered with a heavy metal substance. Electromagnetic coils within the microscope act as 'lenses'. Electrons are beamed through a condenser, which focuses beam of electrons on the specimen. The electrons reflected/emitted from the sample hit an electron detector, which aids in the production of a television-like image. This microscope produces three-dimensional imagery with vivid pictures, and a resolution between 3 nanometers and 20 nanometers. Transmission Electron Microscopy: Specimens are sliced into microscopic sections, stained, and placed in a vacuum. A beam of electrons is then passed through the specimen. Just as in the scanning electron microscope, electrons are concentrated in a magnetic condenser/lens system. The beams are then collected and recorded by the detector. This microscope has a resolution of 2 nanometers.
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