Types Of Microscopes And Magnification Calculations Flashcards
How does an optical microscope work?
It uses light from a light source underneath the specimen, which passes through the specimen
What is a light microscopes resolution, and how does it compare to other microscopes?
- They have a maximum resolution of 0.2 micrometers, so are good to look at whole cells or tissues.
- The wavelength of visible light ranges from 0.4-0.6 micrometers, and so structures closer together then 0.2 micrometers will appear as one object.
What is the maximum useful magnification of a light microscope?
- X1500
- this enables us to see clearly some of the larger structures inside cells, however due to their limited resolution, they cannot magnify any higher while still giving a clear image.
How does a laser scanning confocal microscope work?
-It’s a special type of light microscope which uses laser beams (intense beams of light) to scan a specimen that’s usually tagged with fluorescent dyes.
1) A laser beam is focused through a lens which is aimed at a beam splitter.
2) This splits the beam and some of the light is directed to the specimen, which then causes the dye to fluoresce (give off life)
3) This light is then focused through a pinhole onto a detector. The detector is hooked up to a computer, which generates an image, which can be 3D
4) The pinhole means that any out of focus light is blocked, so these microscopes produce a much clearer image then a normal light microscope
5) They can be used to look at objects at different depths in thick specimens
How do electron microscopes work in general?
Use electron beams instead of light to form an image. They have a higher resolution then a light microscope so give more detailed images.
For the first type of electron microscope, state how it works, what type of image it produces, it’s maximum resolution, maximum magnification and what type of organelles/ specimens it can view
A TRANSMISSION ELECTRON MICROSCOPE:
-works by an electron gun emitting electrons at the top, electromagnets are used to focus the electron beams, the electrons are then transmitted through the specimen on a grid. The denser parts of the specimen absorb more electrons, making them look darker on the image you end up with
-it produces a 2D image which shows the cross section through a sample. It shows the internal structures, as if you’ve taken a slice through the organelle.
- maximum resolution= 0.0002 micrometers. This is the highest resolution because they can distinguish between the smallest objects.
- maximum magnification= more then x1,000,000
-They provide high resolution images, so can be used to look at very small organelles eg ribosomes. The specimens have to be quite thinly sliced and must be dead due to the microscope having to be a vacuum.
For the other type of electron microscope, state how it works, what type of image it produces, it’s maximum resolution, maximum magnification
A SCANNING ELECTRON MICROSCOPE:
-works by scanning a beam of electrons across the specimen (specimen is covered in a thin layer of gold=has large atoms from which electrons bounce off=clear image), this knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image.
-Produces a 3D image which shows the outer surface of a sample, exposing its internal structures.
- maximum resolution of 0.002 micrometers. Resolution is lower then TEM
- maximum magnification of x500,000
What is the purpose of staining samples?
- Staining allows the contrast to increase between organelles, as different parts of the cell absorb different densities of dye. This allows for structures to be seen clearer.
- if an object is completely transparent, it also stops it appearing white
What are some common stains used?
- Methylene blue= used to stain DNA
- Giemsa= used to differentiate between different types of blood cells
- eosin= used to dye cytoplasm
What is the formula for magnification?
Magnification= image size/
Actually size
How do you convert millimetres to micrometers, and reverse?
Millimetres-micrometers= x1000
Micrometers-millimetres=divide by 1000
How do you convert micrometers to nanometers, and reverse?
Micrometers-nanometers= x1000 Nanometers-micrometers= divide by 1000
What is the definition of microscopic?
Need to use a microscope in order to view ‘it’
What is the definition of macroscopic?
Don’t need a microscope to view ‘it’, can be seen with the naked eye
How do you use a scalebar to work out magnification?
1) measure length of scale bar in mm
2) divide our length (mm) by the length the scalebar is representing (micrometers)
3) covert numbers to same units =magnification
