Flashcards in Microscopy (Chapter 1) Deck (30)
What are the four types of microscope?
Compound Light Microscope
Dissecting Light Microscope
Transmission Electron Microscope
Scanning Electron Microscope
What are the two types of light microscope?
Compound and Dissecting
What is the definition of magnification?
The number of times larger an object appears compared to its actual size
What must a specimen be like to be seen with a compound light microscope?
Thin and mostly transparent so that light can pass through it - no detail will be seen if specimens are thick and opaque
What images can a compound light microscope produce?
A 2D image but at a higher magnification than a dissecting light microscope
Describe the characteristics of a dissecting light microscope
They are a special type of binocular microscope used for observations at a low total magnification (x4 to x50)
A large working distance between the objective lens and stage is required
It has two separate lens systems - one for each eye
What images can a dissecting light microscope produce?
A 3D image of an opaque or translucent specimen but at a lower magnification than a compound light microscope
What is the equation for magnification?
magnification = observed size of image (I) / actual size (A)
What is the rule for converting units?
big --> small = multiply
small --> big = divide
What is 1m in mm?
1 / 1000 = 0.001mm
What is 1mm in μm?
1 / 1000 = 0.001μm
What is 1mm in nm?
1 x 10^-6 = 0.000001nm
What is 1μm in nm?
1 / 1000 = 0.001nm
What is the definition of resolution?
The ability to distinguish between two objects very close together
What is the limit of resolution on a microscope?
About half the wavelength of the radiation (type of wave) used to view the specimen
What is the limit of resolution (best resolution) on a light microscope?
Average wavelength of visible light = 400nm
Therefore, the best resolution that can be obtained using visible light = 200nm
What does the limit of resolution mean for viewing an object?
If the object is smaller than the limit of resolution, it can not be seen using that microscope
What is the benefit of having a higher resolution?
More detail can be seen
You can tell if a part of a specimen is separate or a whole
You can see if there are any other parts within a specimen
You can have a higher magnification still with a high resolution
What is an electron microscope?
An electron microscope uses a beam of electrons, instead of light, to produce an image
Why does an EM have a much higher resolution than a light microscope?
Because electrons have a much smaller wavelength than light (approx. 1nm vs 400nm) so their limit of resolution is to a smaller length
What are the two types of EM?
Transmission and Scanning
What happens in a TEM and what can be seen?
The beam of electrons is passed through the specimen before being viewed. Only electrons that are transmitted (pass through the specimen) are seen.
This allows us to see thin sections of specimens and therefore to see inside cells.
What happens in a SEM and what can be seen?
The electron beam is used to scan the surfaces of structures.
Only the reflected beam of electrons is observed.
What is different about a TEM compared to an SEM?
Resolution is approx. 1nm
There is a small depth of field
What is different about a SEM compared to an TEM?
Resolution is approx. 3-20nm
There is a large depth of field
What are the similarities between a TEM and a SEM?
The specimens are stained with metals
The specimens need to be dehydrated and therefore dead