Microscopy Flashcards
How does a microscope work
Light is directed through a thin layer of biological material that is supported on a glass slide
This light is focused through several lenses so that an image is visible through the eyepiece
The magnifying power of the microscope can be increased by rotating the higher power objective lens into place
What are key components of a microscope
The eyepiece lens
The objective lenses
The stage
The light source
The coarse and fine focus
things to be aware when using microscope
When using an optical microscope always start with the low power objective lens
It is easier to find what you are looking for in the field of view
This helps to prevent damage to the lens or coverslip in case the stage has been raised too high
Preventing the dehydration of tissue
The thin layers of material placed on slides can dry up rapidly
Adding a drop of water to the specimen beneath the coverslip
Unclear or blurry images
Switch to the lower power objective lens and try using the coarse focus to get a clearer image
Consider whether the specimen sample is thin enough for light to pass through to see the structures clearly
There could be cross-contamination with foreign cells or bodies
Limitations
Cell structures are 3D and the different tissue samples will have been cut at different planes resulting in this inconsistencies when viewed on a 2D slide
why can electron microscope produce highly detailed images
because they have a higher resolution, or resolving power, than a light microscope
What is resolution
Resolution is the ability to distinguish between two separate points
What happens if two separate points cannot be resolved
producing an unclear image
Why is magnification limited by resolution
there is no point in magnifying an image many times if the resulting image is unclear
why is the resolution of a light microscope is limited by the wavelength of light
The wavelength of light is too long to provide a high resolution
Why do electron microscopes have higher resolution than light microscope
electrons have a much smaller wavelength than visible light
This means that electron microscopes can distinguish between two separate points that are much closer together than the points that can be distinguished by a light microscope
Can electron microscope be capable of higher magnification before image becomes unclear
yes
How do electron microscopes work
Electron microscopes fire a beam of electrons at or through a specimen
The electrons are picked up by an electromagnetic lens which then generates an image
Electron microscopes are useful for looking at organelles, viruses, and DNA, as well as looking at whole cells in more detail
Electron microscopy requires the specimen to be dead which can provide a snapshot in time of what is occurring in a cell
What is Transmission Electron Microscope
TEMs use electromagnets to focus a beam of electrons
This beam of electrons is transmitted through a thin specimen
Denser parts of the specimen absorb more electrons
Denser parts appear darker on the final image, producing contrast between different parts of the object being observed
The internal structures within cells, or even within organelles, can be seen as an 2D image
The resolution of these images are very high
Scanning Electron Microscopes
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 3D images that show the surface of specimens
Since they scan the outside surface it means that the specimens viewed does not have to be thin
The images they form are of a lower resolution than TEMs
