MICROSCOPES Flashcards
What are the 3 types of microscopes ?
. optical microscope
. transmission electron microscope.
. scanning electron microscope.
what is magnification ?
how many times larger and image is compared to the object.
what is resolution?
minimum distance between 2 distinguishing points of objects.
what are optical microscopes
a beam of light is condensed to create an image. it has a poorer resolution due to the light having a longer wavelength. it also has lower magnification. it shows images with color and can view living samples.
what are electron microscopes ?
when a beam of electrons are condensed to create an image. electromagnets are used to condense the beam. they have higher resolutions as the beam of electrons have a shorter wavelength, they also have higher magnification. EM show black and white images and the samples must be in a vaccum , due to this sample must be non living.
what are transmission electron microscopes ?
works by shooting a beam of electrons at a thin sample and detecting the electrons that make it through to the other side.
what are the support and limitations of a transmission electron microscope?
. allows us to view sample in higher magnification and a higher resolution as it has a shorter wavelength.
. the parts of the specimen that absorb electrons appear darker. other parts of specimen that allow electrons to pass through appear lighter
. staining required if image nor visible.
. image viewed is 2D
. image may contain artefacts
. image has no color
. shows internal structure
. must be in a vaccum or air particles would interfere with beam of electrons
how does a scanning electron microscope work?
works by using a focused beam of high energy electrons which reflect off the surface of the structures.
what are the supports and limitations of a scanning electron microscope ?
. gives a 3D image
. sample must be thin as electrons do not penetrate
.lower resolving power than TEM
. can be used on thicker specimens than TEM
. shows only cell surface
what is the difference between a TEM and a SEM ?
TEM works by when electrons are transmitted through a specimen. SEM works by electrons reflecting off a surface.
what is cell fractionation ?
it is the process where cells are broken up and different organelles they contain are separated.
what are the stages in cell fractionation called ?
1) Homogenation
2) filtration
3) Ultracentrifugation
what occurs before cell fractionation ?
The tissue is placed in a cold isotonic buffer solution of the same water potential.
what does the cold isotonic buffer solution do?
it is cold to reduce enzyme activity, it is isotonic to prevent organelles from bursting or shrinking due to osmosis and it is buffered so a constant PH is maintained and the structure of organelles is not affected due to this.
what happens in the
homogenation stage?
the cells are broken down in a homogeniser, this releases the organelles from the cell and results in a fluid known as the homogenate.
