2.1.1. Cell structure - (Microscopes) Flashcards
Definition of magnification
the number of times an image appears larger compared to the actual size of the object
What formula is used to calculate Magnification?
The triangle is Observed size/ Actual size X Magnification
Convert: Centimeter (cm) Millimeter (mm) to Micrometer (um)to Nanometer (nm)
Centimeter X 10 to
Milimeter X 1000 to
Micrometer X 1000 to
Nanometer
Definition of resolution
the ability to distinguish between two different points
Best resolution of a light microscope
0.2 micrometres
Best magnification of a light microscope
x1500
What are Light microscope mainly used to look at?
To look at whole cells or tissues
How does a light microscope work?
> They use light and several lenses in order to magnify.
> Specimens are illuminated with light which is focused using glass lenses
Advantages of a light microscope
> Cheap
Easy to use
Can examine living things
Disadvantages of a light microscope
> Specimens have to be small, thin and transparent
> Have a low resolution due to light
How does a confocal scanning microscope work?
> They use laser lights to scan a specimen thats usually tagged with fluorescent dyes.
The laser beam which is focused through a lens is aimed at a beam splitter
This splits the beam and some of the light to the specimen
When the laser hits the dyes it causes them to give off fluorescent light
This light is then focused through a pinhole onto a detector which is hooked up to a computer, which generates an image.
overall use laser light to scan an object point by point and assemble, by computer, the pixel information into one image
What does a pinhole for laser scanning microscope do?
The pinhole means that any out-of-focus light is blocked, so these microscopes produce a much clearer image
Advantages of a confocal scanning microscope
> Builds a clean 3d image
Can look at objects at different depths in thick specimens
Images are high resolution
Disadvantages of a confocal scanning microscope
> Quite big
> Doesn’t always show full sample
Best resolution of a confocal scanning microscope
20 nanometres
Best magnification of a confocal scanning microscope
x1500
How does a TEM Microscope work?
> They use elctromagnets to focus a beam of electrons which is then transmitted through the specimen to produce a 2D image.
Denser parts of the specimen absorb more elections, which makes them look darker on the image.
Advantages of TEM
> Can look at small organelles
> High resolution
Disadvantages of TEM
> Can only be used on thin specimens
Angles at which the specimen is cut can affect how they appear
Specimen are dead as they must be viewed in a vacuum
Best resolution of TEM
0.0002 micrometres or 0.2 nm
Best magnification of TEM
more than 1,000,000
How does a SEM work?
They scan a beam of electrons across the specimens. This knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image.
Advantages of a SEM
produces a 3D image
Disadvantage of SEM
> Have a lower resolution than TEMs
Specimens are dead as they must be viewed in a vacuum
Only shows the surface of cells
Best resolution of SEM
0.002 micrometres
Best magnification of SEM
less than 500,000
Similarities of SEM & TEM
> Both are large and very expensive
> Need a great deal of skills and trainning to use
