magnification Flashcards
magnification definition
- How many times bigger an image appears, compared to the real specimen.
Resolution definition
The ability of a microscope to distinguish between 2 points that are close together.
cm to mm
x10
mm to micrometer
x1000
micrometers to nanometres
x1000
nanometres to micrometers
/1000
micrometers to mm
/1000
mm to cm
/10
uses of a light microscope
uses light rays to observe object
advantages of light microscope
- Can observe living things
-Does not use harsh chemicals - Easy to set up and use
- Cheap and portable
Disadvantage of light microscope
- Low magnification (up to 2000 times)
- Low resolution
Uses of transmission electron microscope
- Uses focussed beams of electrons through sections of tissues.
Uses of scanning electron microscope
Uses focussed beams of electrons reflected off the tissues.
Advantages of transmission and scanning electron microscope
- High magnification
- High resolution
- Can see details inside cells - T.E.M
- Can see details of the surfaces of the structures S.E.M
Disadvantages of TEM and SEM
-Can only see dead materials
- Harsh chemicals used in preparation which can cause artefacts
- Expensive
Uses of scanning confocal microscope
Uses a laser beam of light to illuminate chemical stains within the specimen. These then fluoresce.
Advantages of laser scanning confocal microscope
- Can see living cells
- Can observe cell processes by tracking molecules
- Higher resolution than light microscope
Disadvantages
- More expensive than light microscope and more complex
How do we use optical microscope?
- Clip the slide you prepared onto stage.
- Select lowest-powered objective lens.
- Use course adjustment knob to move objective lens down to just above slide.
- If you need to see slide with greater magnification, swap to high-powered objective lens and refocus.
How to prepare microscope slide?
- Start by pipetting a small drop of water onto centre of slide.
- Use tweezers to place thin section of specimen on top of water drop.
- Add stain to sample.
- Finally, add cover slip. Stand slip upright on slide, next to water droplet. Then carefully tilt and lower, so covers specimen. Try not to get air bubbles, as it will obstruct view of specimen.
Why do we stain specimen?
- Adds contrast to image, some parts of sample will take up stain, other parts won’t.
-Makes image visible.
Why do we use a thin section of specimen on slide?
-To let light through it, so it can be seen more clearly.
Explain gram stain technique.
-Apply crystal violet.
-Apply iodine to fix dye.
- Gram positive bacteria will appear blue, purple.
- Gram negative doesn’t take up crystal violet, so add safranin, which is a counter stain, will then turn red.
