BIOLOGY 2.1
EMILY KINZLER
Emily Kinzler
, RANGE OF OBJECTS SEEN WITH/WITHOUT MICROSCOPES
MAGNIFICATION electron microscope - atom, lipids, ribosome, protein, influenza, mitochondria, chloroplast, bacterium, human cheek
cells, human ovum, onion epidermis cell, amoeba
how much bigger object appears in comparison to og size light microscope - influenza, mitochondria, chloroplast, bacterium, human cheek cells, human ovum, onion epidermis
microscopes produce linear magnification cell, amoeba
linear magnification = x100 = 100x wider, 100x longer
SCANNING ELECTRON MICROSCOPES
electrons dont pass through spec (whole)
RESOLUTION instead causes secondary electrons to bounce off surface + focus onto a screen
distance at which two points seen as seperate 3d image
mag x15 - x200000
B&W
add false colour on computer
spec needs to be placed in vacuum + covered in thin film of metal
OPTICAL MICROSCOPES electron microscopes - large, expensive, need lots of training to use, spec must be dead as viewed in
vacuum, metallic salt stains can be hazardous to user
cheap
easy to use
portable, can use in field/lab
can study whole living spec
relies on lenses to focus beam of light
mag upto x1500 (-x2000)
so can see larger structures in cells
limited resolution MICROSCOPES
uses visible light so has wavelength of 400-700nm
so, structures closer than 200nm appear as one (0.2 micrometres)
ribosomes are 20 nm in diameter so cant be seen
1. place spec on slide + clip into place
2. rotate nosepiece so lowest power objective lens over spec
TRANSMISSION ELECTRON MICROSCOPES
3. adjust coarse focus while looking in eyepiece for focus spec must be chemically fixed - dehydrated + stained
4. while viewing image adjust iris diaphragm for optimum light beam of fast travelling electrons passes through spec stained w metal salts
5. ensure spec directly over hole in stage, adjust fine focus some electrons pass through + focused onto photographic plate/screen
6. repeat 5 w/ higher mag objective lens
! forms 2d B&W image - electron micrograph
mag x2mil (-x50mil)
CALCULATING MAGNIFICATION
total mag = mag of objective lens x mag of eyepiece lens ELECTRON MICROSCOPES
photomicrograph - image seen w/ optic microscope uses beam of electrons w wavelength of 0.004nm
so have greater res than optical
electrons fired from cathode, focused by magnets (not glass lenses like optical) onto a
photographic plate
LASER SCANNING MICROSCOPES has better resolution than optical as fast travelling electrons’ wavelength is x125000 smaller
than center of visible light spectrum
aka confocal microscopes
use laser light to scan object point by point, use computer to put pixel info to image on computer
high resolution
high contrast
has depth selectivity so can focus at structures @ diff depths in a spec
can observe whole living specs
used to give swift diagnoses in patients
