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