Cell structure - Microscopy Flashcards
how does a light microscope work
the light microscope focuses the light onto the specimen and then magnifies the image through a series of lenses
describe how to use the microscope
clip the slide onto the stage
turn on the light
select the lowest powered objective lens
use the coarse adjustment knob to move the objective lens to just above the slide
look down the eyepiece and adjust the focus by moving the lens away from the slide using the fine adjustment knob until a clear image appears
what are stains
coloured chemicals that bind to molecules in a specimen
what are the three uses of stains
makes cells visible
increases contrast (as different components of the cell take up different amounts of the stain)
detail inside cells can be seen eg organelles can be identified
2 examples of stains
methylene blue: stains living cells blue
iodine solution: stains starch grains blue black
describe the process of differential staining
using more than one chemical stain. different stains bind to specific structures. this can be used to show contrast between organelles, tissues and microorganisms
define magnification
the number of times larger an image is compared with the actual size of the object
what is the equation for magnification
M=I/A
define resolution
the ability to distinguish between two separate points that are very close together
why is a high resolution good
more detail can be seen with a higher resolution, resolution gives clarity
what is the max resolution of a light microscope
200nm
what is the max resolution of an electron microscope
0.2nm
how do electron microscopes create magnified images
by using electrons instead of light waves
why must samples be prepared carefully in an electron microscope
to withstand the vacuum inside the microscope
how do electron microscopes work
the air is pumped out the microscope and a beam of electrons is fired through a series of electromagnetic lenses which focus the electrons. the electrons are detected and turned into a black and white image (electron micrograph).
why is false colour sometimes added to electron microscope images
to make them easier to understand
how must the sample be prepared in a scanning electron microscope
sample must be dried carefully and coated thinly in gold
how is the sample prepared in a transmission electron microscope
sample must be sectioned thinly
how do SEM work
the beam moves back and forth across the specimen. electrons knocked off the specimen are detected
what is the resolution of SEM
2nm
what is the maximum magnification of SEM
x200,000
describe the image produced by a TEM
2D, high resolution, internal structure
how do TEM work
use electromagnets to transmit a beam of electrons through a specimen; denser parts of the specimen absorb more electrons, meaning that denser parts appear darker on the final image
describe the image produced by a SEM
3D, surface of specimen
what is the maximum magnification of TEM
x2,000,000
what is the resolution of TEM
0.2nm
what are SEM used to study
the surfaces of objects
what are TEM used to study
the ultrastructure of cells
compare the wavelengths of light and electron microscopes
light:400-700nm
electron:0.004nm
compare the maximum magnifications of light and electron microscopes
light:x2000
SEM:200,000
TEM:2,000,000
compare the resolution of light and electron microscopes
light:200nm
SEM:2nm
TEM:0.2nm
compare how focusing is carried out by light and electron microscopes
light: by glass lenses
electron: electromagnetic lenses
compare the costs to purchase and operate in light and electron microscopes
light: cheap
electron: expensive
compare the sizes of light and electron microscopes
light: small
electron: large
compare how materials are prepared in light and electron microscopes
light: easy
electron: hard
in which microscope is a vacuum required
electron
are the materials distorted by the preparation in light and electron microscopes
light: no/maybe
electron: yes
are the specimens living or dead in light and electron microscopes
light: living or dead
electron: dead
is colour observed in light and electron microscopes
light: yes
electron: no
what is an eyepiece graticule
a printed scale in the microscope eyepiece
how many units is an eyepiece graticule divided into
100 EPU
what is a stage micrometer
a microscope slide which has a fine and accurate scale engraved on it
how long is the micrometer scale usually used
1mm
how many units is the micrometer scale usually divided into
100
how long is each small division on a stage micrometer
10 micrometres
does the calibration of the eyepiece graticule have to be done separately for each lens
yes
describe simply how to calibrate an eyepiece graticule
line the scale on the stage micrometer with the scale on the eyepiece graticule and count the number of EPU that correspond to 1mm on the stage micrometer.
what is the value of one EPU in micrometres for low power objective lens (x40)
25
what is the value of one EPU in micrometres for medium power objective lens (x100)
10
what is the value of one EPU in micrometres for high power objective lens (x400)
2.5
give ways of improving the microscopy practical
use a wet mount
cut finely so you can see individual layer of cells
squash slide to prevent dehydration/distortion
