Microbiology: A Human Perspective Ch. 3
Micrometer
(cell size) 1 millionth of a meter
Nanometer
(virus size) One billionth of a meter
Frog Egg Size
1 to 2 mm
Millimeter
1/1000 of a meter
Virus size
20-400 nm
compound microscope
A light microscope that has more than one lens.
resolving power
A measure of the clarity of the image; it is the minimum distance two points can be separated and still be distinguished as two separate points
light microscope
An optical instrument with lenses that refract (bend) visible light to magnify images of specimens---1,000x
refraction
Bending of light
4x, 10x, 40x, 100x
Magnification of a light microscope
ocular lens
Magnifies the object, usually by 10X. Also known as the eyepiece, this is the part you look through to view the object
objective lens
Magnifies the specimen
electron microscope
Microscope that forms an image by focusing beams of electrons onto a specimen---100,000x
bright-field microscope
Microscope which creates a magnified image against a bright background. Most common variation of the light (optical) microscope.
refractive index
Speed of light in substance. Air ~1, Oil ~1.5, Glass ~1.5. Oil matches refractive index of glass so light doesn't "bend". Glass to air means light will "bend" and get lost.
illuminator
The light source for the microscope.
atomic-force microscope
Uses a pointed probe and traverses the tip of the probe lightly on the surface of the specimen, rather than at a distance. Observe living specimens at the molecular and atomic levels.
Magnification---Increase in apparent size of an organism Resolution---Minimum distance between 2 points at which those points can still be observed as separate objects
What is the difference between magnification and resolution?
0.2 um---depends on the quality and type of lens, the wavelength of light, the magnification, and how the specimen has been prepared
What is the limit of resolution of a light microscope? Why (what actually limits the resolution)?
Red light has a longer wavelength---But, the shorter wavelength (blue light)=higher resolution, which allows you to resolve points that are closer together, so it is better to use blue light.
Which has a longer wavelength, red or blue light? Which would be better to use with a light microscope? Why?
Because electrons have a wavelength about 1,000 times shorter than visible light, so the resolving power is about 1,000-fold more than light microscopes (0.3x 10^-3 um)---but the specimen must be in a vacuum, which is a drawback
Why can the electron microscope achieve such a high resolution?
To displace the air between the lens and the specimen---the oil prevents refraction b/c it has nearly the same refractive index as glass
Why do we use immersion oil with the 100x objective lens?
condenser lens
concentrates the light and makes illumination of specimen more uniform
Human cell size
most from 10 - 15 μm in diameter
Bacteria cell size
vary greatly - largest known size of period - smallest are about 0.5 to 1 micrometer
