microbiology ch4 Flashcards
light
affects our ability to visualize objects with the human eye
wavelength
*length of a light ray
*represented by Greek letter lamda
*equal distance between two adjacent crests or two adjacent troughs of a wave
resolution
*ability to see two items as separate and distinct units rather than one fuzzy overlapping image
*light must pass between objects to be seen as separate
*key: get light of short enough wavelength to fit between objects.
reflection
*light strikes an object and bounces back- reflection has occurred.
transmission
*the passage of light through an object
*most microorganisms will make use of transmitted light
absorption
*light rays neither bounce off nor pass through an object
*light rays are taken up by an object- absorption has occurred
iluminescence
*absorbed light rays are changed into longer wavelengths and reemitted
refraction
*bending of light as it passes from one medium to another of differing density
*gives rise to an angle of refraction or the degree of bend
index of refraction
*measures the speed at which light passes through a material
*substances that have different indices of refraction, light will bend as it passes from material to material
*can cause loss of light and blur an image
immersion oil
*oil joins the slide and lens together
*prevents refraction of the image
staining
*increases differences in indices of refraction
*makes it easier to observe detail
light microscope
*any microscope that uses visible light to make specimens observable
compound microscope
*a microscope with more than one lens
*gives distortion free image
monocular vs binocular lens
*monocular- single eyepiece
*binocular- two eyepieces
blue filter
*filters out long wavelengths of light, leaving shorter wavelengths and improves resolution
condenser
*converges the light beam so that it they pass through the specimen
iris diaphragm
controls amount of light that passes through the specimen to the objective lens
objective lens & total magnification
*magnifies the image before it passes through the body to ocular lens
* Scan- (4X) x (10X) = 40X total mag.
*Low power- (10X) x (10X) = 100X total mag.
*High-dry power- (40X) x (10X) = 400X total mag.
*Oil immersion- (100X) x (10X) = 1000X total mag.
mechanical stage
allows precise control of moving the slide
focus adjustment knobs
*coarse adjustment- changes distance between objective lens and specimen rapidly
*fine adjustment- changes the distance between the objective lens and specimen slowly
dark field microscopy
*microscope adapted for dark-field illumination have condenser that causes light to reflect off the specimen at an angle
*a light object is seen on a dark background
phase-contrast microscopy
*used to observe live specimen
*light is slowed down and diffracts the change in light speed, seen as different degrees of brightness
*short depth of field, can produce a nearly 3-D image.
fluorescent microscopy
*ultraviolet light used to excite molecules, so they release light of longer wavelengths
*produces a brilliant shade of orange, yellow, yellow green
digital microscopy
*they have auto-focus, auto-aperture, auto-light, motorized stage and magnification changers
*just plug in and power on
*magnification is limited on digital microscopes