microscope Flashcards
define magnification
the number of times larger an image is compared with real size of the object
define resolution
the ability to distinguish between two separate points. if two points can’t be resolved, they will be seen as one point
what is the cell theory
all organisms are composed of one or more cells
the cell is the basic organisational unit of life
all cells arise from pre-exisiting cells
name three types of microscope
light
transmission electron microscope
scanning electron microscope
how does the light microscope work
has 2 lenses [eyepiece and objective lens]
how does electron microscope work
a beam of electrons with wavelength of less than 1nm is used to illuminate
a vacuum inside the machine ensures the beam travels in a straight line
the pros of electron microscope
can see details of organelles
much higher resolution than light microscope
can magnify objects more than 500000x
two main types - TEM,SEM
cons of using electron microscope
very large, must be operated in special rooms
affected by magnetic fields
preparation of material is lengthy, requires expertise and sometimes complex equipment
all images are black and white
expensive to purchase and operate
beam can damage specimen
complex specimen prep process can damage the specimen
how can the specimen be damaged
fixation using chemicals or freezing
staining with heavy metals
dehydration with solvents
TEM samples then set in resin and may be stained again
SEM samples may be fractured to expose the inside and then coated with heavy metal
how does scanning electron microscope work
scan a beam of electrons across the specimen from above
the electrons are scattered by the specimen according to the contours of the specimen surface
a computer can then analyse the pattern of scattered electrons to build up a 3d image
image show the surface of a specimen and can be 3d
which microscope has the greatest magnification and resolving power
transmission electron microscope
how does transmission electron microscope work
use electromagnets to focus a beam of electrons which is then transmitted through a thin section of specimen and focussed to produce an image
denser parts of the specimen absorb more electrons which then makes them look darker on the image
other parts allow the electrons to pass through and so appear bright
can only be used on thin specimens
pros of using a light microscope
quick and simple to set up
inexpensive
cons of using a light microscope
low resolution
low magnification
