Week 2 - Light & Seeing Cells Flashcards
challenges associated with seeing cells
- limit of resolution
- transparency/ translucence
- thick / opaque samples
two-eyed seeing
indigenous ways of knowledge & western ways of knowing
reflection
light bounces off
absorption
light energy absorbed
transmission
light passes through
refraction
transmission w change of dir.
- helps magnify through lenses … can enhance contrast
spectrophotometry
measuring absorbance and transmittance of light
light microscopy
using refracted, transmitted & absorbed light to view features of cells
- can magnify by about 1000x
brightfield microscopy
most light transmitted through specimen (appears transparent), except what is absorbed (appears dark)
darkfield microscopy
only refracted (scattered) light makes it to our eyes (appears bright)
- most of specimen appears dark
phase contrast microscopy
directly transmitted light (no phase shift) doesn’t make it to our eyes / phase plate (detector)
only scattered light (phase shifted) makes it to our eyes (appears bright)
L.M. magnification =
objective x ocular (eyepiece)
photon
unit of light energy
fluorescence microscopy
takes advantage of molecules that can fluoresce
fluorescence
emitting a specific wavelength of light when excited by a lower wavelength (increase energy)
emitted light is always…
lower energy than excitation light
Resolution
min. distance at which 2 points are distinguishable
eye = ~100um
light microscope= 0.2um
lower resolution = improved view
confocal microscopy
uses laser light
improves resolution about 10-fold
electron microscopy
beams of electrons on/ through a specimen to visualize subcellular structures
substantially improves resolution
what can we see w light microscopy
euk&prok cells, some organelles (mitos, nucleus, chloroplasts)
not: membranes, ribosomes
what can we see w electron microscopy
cell ultrastructure, organelle ultrastructure, membranes, ribosomes
