Lab Notes and Procedures-01 Biology 1004
North Arkansas College
Topic: Microscopy
(Experiment 1, Page 5-18)
- The human eye is so constructed that we cannot see objects smaller than 30 m m.
1 meter = 39.37 inches
1 centimeter (cm) = 1/100 of meter
1 millimeter (mm) = 1/1000 of meter
1 micrometer (m m) = 1/100 of millimeter
1 nanometer (n m) = 1/1000 of micrometer
- Frog egg is 1-5 mm.
- Animal or plant cell - 10-100 m m.
- Cell nucleus - 10 m m.
- Bacteria - 0.1 m m wide by 1-2 m m long.
- Ribosome - 20 nm; Virus - 50 nm.
- It is necessary to be able to magnify smaller cell or components of those cells. This requires glass lens (biconvex) and light sources of various wavelengths.
- The most important property of any lens or microscope is it’s resolving power. Resolving power - the ability to distinguish between two dots that are side by side, or the diameter of the smallest observable object.
- Maximum magnification with the unaided eye depends of two things, e.g. how far object is from eye, and the angle the object makes with the eye - 10 inches from eye.
- Microscope uses lens that make objects appear closer than 10 inches from the eye, and can still focus on it. The simplest microscopes are magnifying glasses: 10X, 20X.
- Resolving power - Wavelength of light
Numerical aperture
Numerical aperture depends on the focal length of lens that is used. The focal length is the distance between a lens and where the focal point occurs.
Three Major Types of Microscopes
- Simple Microscope - One lens, a single magnification takes place (like magnifying glass).
- Electron Microscope - Platinum filament which when heated gives off electrons as wavelengths of light. They are short wavelengths and produce high magnifications. Produce magnifications of about 20,000 to 150,000; pictures produce 1-3 million magnifications.
- Compound Brightfield Microscopes -
- Uses two or more lens and produces multiple magnifications.
- Wavelength of light is visible light (600 m m long).
- All contain an eyepiece or ocular: 10X.
- Also contain a revolving nosepiece with different objective lens associated with it.
Low Power Lens (yellow) = 10X; coupled with eyepieces gives total magnification of 100X.
High Dry Power = 40X; total magnification of 400X.
Oil immersion = 100X; total of 1000X.
The Compound Light Microscope allows us to see objects with a diameter of 0.2 m m.
