Microscopes
MICROSCOPES Magnification: Resolution: Field of View: Describes the visual picture seen when looking through the eyepiece of the microscope 7X 45X 112.5X 225X
1 st crude microscope made by the Dutchman Van Leeuwenhoek In the 17th century, amateur scientist Anton Leeuwenhoek enlightened the world about what he dubbed animacules such as protozoa found in standing water. Using microscopes he made himself, Leeuwenhoek wrote up what he viewed in pond water, plant material, even gunk scraped off his teeth. He was the first to identify sperm and red blood cells.
Leeuwenhoek s Microscope
2 MainTypes of Microscopes Light Electron Stereomicroscope Compound Scanning Transmission Scanning-Tunneling
COMPOUND LIGHT MICROSCOPES Can magnify up to 1,000x Powerful enough to view algae, protozoa Some powerful enough to view bacteria CANNOT view tiny parts of cells (organelles) or view viruses in detail Sample must be larger than 0.2mm Samples must be stained 2D image of dead or alive
Compound Light Microscope Diatom Paramecium 25x mag. Euglena 400x mag.
Compound Microscope Images
UD Virtual Compound Microscope
STEREOMICROSCOPE Also called a dissecting microscope Magnifies 10X Reserved for larger objects that can be seen with your eyes but may need magnification for details Image is 3D
Stereomicroscope Details of a spider s foot Detail of concrete sample Details of a fly tongue Moth pupa
Electron Microscopes Developed in the 1940 s View extremely tiny objects (organelles, viruses) Use streams of electrons instead of light to create images No living samples Scientists don t see the images directly through lenses as they do with light microscopes. Instead, the machinery of the electron microscope generates a picture on a TV or computer screen.
SEM Scanning Electron Microscope The specimen is usually coated with an ultra-thin layer of heavy metals/ gold. The electron beam scans over the surface of the specimen, exciting electrons on the surface. Especially useful for studying the surfaces and structures of cells First commercial SEM was built in 1965
Scanning EM 3D image Specimens not sliced for viewing 100,000X magnification Cannot be used to view living specimens Daisy Petal
Bread mold (1200x) Penicillium is the stuff the antibiotic is made from and grows not only on bread but on citrus fruits as well.
Start here! Virtual Scanning Electron Microscope
TEM Transmission Electron Microscope Transmit electron beams through a thin section or slice of a specimen to create an image. TEMs are particularly useful for studying the insides of cells. Cannot be used to study living cells 2D image with 200,000X magnification First built in 1931
TEM Mitochondria Microtubules Cardiac muscle
Display things as minute as the individual atoms on an object s surface. 100 million X They use an electrically charged tip that is placed within nm of the surface of the specimen. Electrons jump between the tip and the specimen surface in what s called the tunneling current. As the tip is moved back and forth across the specimen, the current varies according to whether the tip is right over an atom or over the space or trough between atoms. A computer creates an image based on these differences in current. STM Scanning-Tunneling Microscope
The STM can even move atoms about. The image below depicts the results of such a process. Xenon atoms on a nickel substrate spell IBM
A scanning tunneling microscope image of 5 nm gold nanoparticles Nano- means 1/1,000,000,000th
Atomic Force Microscope IBM article 8/28
Light Microscopes (compound) Specimen mounted on a glass slide on stage Must be thinly sliced or very small Pair of lenses Ocular lens (eye piece) 10X Objective lens (nose piece)
Magnification determined by multiplying power of the objective & ocular lenses Maximum magnification is around 2000X for the best microscopes
Different parts of a microscope
Magnification Magnification is represented by a whole number that is sometimes followed by an x Record the following in your lab notebook: Magnification of eyepiece? Magnification of scanning objective? Magnification of low power objective? Magnification of high power objective?
Total magnification To calculate the total magnification, multiply the magnification of the eyepiece times the magnification of the objective to calculate total magnification Record the following in your lab notebook: Total magnification under scanning? Total magnification under low power? Total magnification under high power?
Drawing specimens Always use pencil so you can erase and shade Draw a circle first which represents your field of view (the area you can see while looking through your microscope) Draw your specimen to scale (how big is it compared to your field of view) Label each drawing with the name of the specimen and the total magnification
Focusing a Microscope On low power, use the Coarse adjustment knob to focus On high power, use the fine adjustment knob to focus
5 grains of salt Using the rules for drawing a specimen, draw a grain of salt under scanning, low, and high power Create your slide, by slightly wetting your fingertip and gently rubbing the slide with it. Now sprinkle five grains of salt on the moisture. Record your observations/ sketches in your lab notebook.
Making a wet mount slide Procedure Place a drop of water on the center of a clean dry slide Place the specimen in the middle of the drop. While holding the cover slip upright, carefully place one edge of the cover slip next to the water. Slowly lower the upper edge of the cover slip onto the water. The objective is to minimize or eliminate air bubbles under the cover slip. You might find it helpful to use one toothpick to hold the lower edge in place, while using another to carefully lower the slip into place. Questions for Thought Why would you want to wet mount a specimen? (To increase its translucency and to make it easier to stain. It also has a tendency to flatten the subject, making it easier to view.)
Common Metric Prefixes used in Biology Kilo- means 1000 Centi- means 1/100 th Milli- means 1/1000 th Micro means 1/1,000,000 th Nano- means 1/1,000,000,000th
Cell sizes
Cell Size Interactive Site How Big is a...?