cells and microscopes 2.1.1 Flashcards
what is average diameter of eukaryotic cell
20-40 micrometers
what is average diameter or prokaryotic cell
0.5-5 micrometers
what is average diameter of prokaryotic ribosomes
18 nanometers
what is average diameter of eukaryotic ribosomes
22 nanometers
what resolution can be achieved by using a light microscope
200 nanometers
what resolution can be achieved using a transmission electron microscope
0.05-1.0 nanometers
how does a light microscope work
light is passed through a specimen and focused through glass lenses which projects a magnified image
how is a dry mount prepared
specimenis sectioned and placed onto centre of slide, coverslip is placed over sample
how is a wet mount prepared
specimens are suspended in liquid,coverslipis placed on from an angle.
what organelles could be visible with a light microscope
optical microscopes can be used to observe eukaryotic cells, their nuclei and possibly mitochondria and chloroplasts
Optical microscopes cannot be used to observe smaller organelles such as ribosomes, the endoplasmic reticulum or lysosomes
what is the maximum magnification of a light microscope
The maximum useful magnification of optical microscopes is about ×1500
why is the resolution of a light microscope so poor
it is limited by the large wavelength of light
why do electron microscopes have much better resolution
A beam of electrons has a much smaller wavelength than light, so an electron microscope can resolve (distinguish between) two objects that are extremely close together
what resolution can be achieved with a electron microscope
0.2 nm
what is the most useful magnification of a electron microscope
×1,500,000
how do transmission electron microscopes work
TEMs use electromagnets to focus a beam of electrons
This beam of electrons is transmitted through the specimen
Denser parts of the specimen absorb more electrons
This makes these denser parts appear darker on the final image produced (produces contrast between different parts of the object being observed)
what are some advantages of TEM
They give high-resolution images (more detail)
This allows the internal structures within cells (or even within organelles) to be seen
what are some disadvantages of TEM
They can only be used with very thin specimens or thin sections of the object being observed
They cannot be used to observe live specimens (as there is a vacuum inside a TEM, all the water must be removed from the specimen and so living cells cannot be observed, meaning that specimens must be dead, unlike optical microscopes that can be used to observe live specimens)
The lengthy treatment required to prepare specimens means that artefacts can be introduced (artefacts look like real structures but are actually the results of preserving and staining)
They do not produce a colour image (unlike optical microscopes that produce a colour image)
how do scanning electron microscopes work
SEMs scan a beam of electrons across the specimen
This beam bounces off the surface of the specimen and the electrons are detected, forming an image
This means SEMs can produce three-dimensional images that show the surface of specimens
what are some advantages of scanning electron microscopes
they can be used on thick or 3-D specimens
They allow the external, 3-D structure of specimens to be observed
what are some disadvantages of scanning electron microscopes
They give lower resolution images (less detail) than TEMs
They cannot be used to observe live specimens (unlike optical microscopes that can be used to observe live specimens)
They do not produce a colour image (unlike optical microscopes that produce a colour image)
how does a laser scanning confocal microscope work
laser beam is focused through lens, aimed at a beam splitter which directs some of the laser onto the specimen, when laser hits dyes they give off fluroescent light which is focused through a pinhole onto a detector.
Multiple depths of the tissue section/organisms are scanned to produce an image
what are some advantages of the laser scanning confocal microscope
They can be used on thick or 3-D specimens
They allow the external, 3-D structure of specimens to be observed
Very clear images are produced. The high resolution is due to the fact that the laser beam can be focused at a very specific depth
You can even see the structure of the cytoskeleton in cells
what are some disadvantages of the laser scanning confocal microscope
It is a slow process and takes a long time to obtain an image
The laser has the potential to cause photodamage to the cells
what is the point in staining
provides contrast to differentiate between different structures in the sample
what is differential staining
where multiple different stains are used, each stain binds to a different cell structure, stains each structure differently, so the structures can be easily identified.
what does methylene blue stain
multipurpose stain, stains DNA blue
what is iodine used to stain
stains starch turning it blue/black, can be used to stain cellulose
what can be used to stain cytoplasm
Eosin (Dark red/pink)
what are 2 common stains
Toluidine blue and phloroglucinol
why are stains. used for electron microscopes
When using Transmission electron microscopes (TEMs) the specimen must be stained in order to absorb the electrons
Unlike light, electrons have no colour
The dyes used for staining cause the tissues to show up black or different shades of grey
Heavy-metal compounds are commonly used as dyes because they absorb electrons well
