Cell Structure And Microscopy: Microscopy Flashcards
What are microscopes used for?
Used to analyse cell components and observe organelles
What is magnification?
How many times bigger the image produced by the microscope is than the real life object.
What is resolution?
The ability to distinguish between two objects that are close together
TotalMagnification equation:
Total magnification = eyepiece lens magnification x objective lens magnification
Actual size of image equation:
IAM triangle = Actual Size of Image = Image Size/ Magnification
Advantages of Light microscopes:
- Small and portable
- Inexpensive
- Specimen preparation is straightforward
- Specimen can be dead or alive
Disadvantages of Light Microscopes:
- Light wavelength is large which means less of an ability to resolve objects
- Limited organelles that can be viewed
- Low magnification
- Low resolution
How do SEM’s work?
They scan a beam of electrons across the surface of the specimen. This bounces off the surface and the electrons are detected, forming an image. SEMs therefore form 3D images that show the surface of a specimen.
Advantages of SEM’s
- Can be used on thick or 3D specimens
- Allow external 3D structures to be observed
- High magnification: x500,000 or less
Disadvantages of SEMs
- Lower resolution than TEMs
- Cannot be used on live specimens
- Don’t produce colour images
How do TEMs work?
TEMs use electromagnets to focus a beam of electrons, which is transmitted through the specimen. Denser parts of the specimen absorb more electrons, making them appear darker on the final image.
Advantages of TEMs
- Higher resolution = more detail
- Internal structures can be seen
- Magnification is x1,000,000 or more
Disadvantages of TEMs
- Only used with very thin specimens or thin sections of an object
- Cannot be used to observe live specimens because of the vacuum inside the TEM plus all water must be removed from the specimen
- Lengthy treatment required to prepare specimens. Artefacts could be introduced.
- Don’t produce colour images
- 2D
What is an artefact?
These look like real structures but are actually the results of preserving and staining. E.g. air bubbles under a coverslip
How do Laser Scanning Confocal’s work?
Cells are viewed stained with fluorescent dyes. A thick section of tissue or small living organisms are scanned with a laser beam (focussed light). The laser beam is reflected by the fluorescent dyes. Multiple depths of the tissue section are scanned to produce an image (as if the laser builds the image layer by layer).
