Lecture 3 Flashcards
Why is staining important
improves CONTRAST between different cells/features
resolution
The ability to distinguish between two adjacent objects as distinct and separate
resolution is a function of..
the physical properties of light
resolution is determined by..
the wavelength of light used and numerical aperture of lens
resolution is _________________ to wavelength
inversely proportional
shorter wave length =
better resolution
Limit of resolution for light microscope is about…
o.2 um
Compound light microscopes use….. to illuminate cells
visible light
4 types of light microscopy
- bright-field
- phase contrast
- dark-field
- fluorescence
bright field microscopy
specimens are visualized because of differences in contrast (density) between specimen and surroundings
total magnification =
objective magnification x ocular magnification
Maximum useful magnification is…
~2000x
Phase-Contrast Microscroscopy was invented in 1936 by…
Frits Zernike
Phase Contrast Microscopy
- amplifies differences in the refractive index of cell and surroundings;
- improves contrast without use of stain
- allows for visualization of live samples
- dark cells on a light background
dark field microscopy
light reaches the specimen from the sides
- good for observing motility
- appears light on a dark background
fluorescence microscopy
used to visualize specimens that fluoresce
- may fluoresce naturally of after staining
- widely used for enumerating bacteria
differential interference contrast microscopy
uses a polarizer to create two distinct beams of polarized light
-gives structures such as endospores, vacuoles, and granules a 3D appearance
atomic force microscopy
-a tiny styles is placed close to a specimen and it measures weak repulsive forces between it and the specimen
confocal scanning laser microscopy
-computerized fluorescence microscope coupled with a laser source to generate a 3D image
electron microscopy
electron microscopes use electrons instead of photons to image cells and structures
transmission electron microscopy
operates in a vacuum and is used to examine cells and cell structure at very high magnification and resolution
- visualization at a molecular level
- specimen must be very thin and stained
scanning electron microscopy
for observing external features
-specimen is coated with a thin film of heavy metal and an electron beam scans object to form image
morphology
cell shape
coccus
spherical
rod
cylindrical
spirillum
spiral
cells with unusual shapes
spirochete, appendages bacteria, and filamentous bacteria
Morphology typically ___________ physiology, ecology, phylogeny, etc. of a prokaryotic cell
does NOT predict
May be _________ _______ involved in setting the morphology
selective forces
