Methods of studying cells and magnification Flashcards
Magnification definition?
The degree to which the size of an image is large than the object itself
Resolution/resolving power definition?
The minimum distance apart that 2 objects can be in order for them to appear as separate items.
- determined by wavelength of light/beam of electrons
Light microscopes?
- beam of light condensed to create image
- lower resolution as longer wavelength (max = 0.2 micrometres)
- lower magnification (max useful magnification = x 16500)
- colour images
- can view living samples
- can’t see organelles smaller than 0.2 e.g. ribosomes/ER/lysosomes
Electron microscopes?
- beam of electrons condensed using electromagnets to form an image
- higher resolution as electrons hv shorter wavelength (max resolution = 0.0002 micrometres)
- higher magnification (max useful magnification = x 1,500,000)
- black and yt images produced
- sample must be in vacuum so - non-living (cos electrons absorbed by air & not reach sample)
Transmission electron microscopes (TEMs)?
- beam of electrons -> transmitted thru stained extremely thin specimen
- denser parts of specimen absorb more electron so - look darker on image
- image produced is 2D & shows detailed images on internal structure of cells
Scanning electron microscopes (SEMs)
- specimens don’t need to be thin as electrons NOT transmitting thru instead…
- electrons beamed onto surface & electrons r scattered in diff ways depending on contour (depths)
- 3Dimage
Advantages of TEMs v SEMs
TEMs: give high resolution images so - shows small objects
SEMs: can be used on thick specimens
- can be 3D
Disadvantages of of TEMs v SEMs
TEMs: only used on thin specimens
- only used on non-living specimens
SEMs: give lower resolution images than TEMs
- only used on non-living specimens
Magnification formula?
I = AM
image size = actual size x magnification
converting units?
m -> dm = x10
m -> cm = x100
m -> mm = x 1000
m -> microm = x 1,000,000
m -> nm = x 1 bil
Eye piece graticule?
inside of light microscopes - a glass disc - has scale etched onto it to measure size of objects
- each time change objective lens (so- magnification) - hv to calibrate eyepiece to work out what dis between each div represents at that magnification
Calibration?
- using a stage micrometer
- place on stage
- scale usually 2mm long & sub-divisions r 10 microm apart
Steps on calibration?
- Line up stage micrometer & eyepiece graticule whilst looking thru eye piece
- Count how many divs on eyepiece graticule fit into 1 div on micrometer scale (micrometer is bigger)
- Each div on micrometer = 10microm - use to calculate what 1 div on eyepiece graticule is at current magnification
- Measure size of cells/organelles
Rules for biological drawings?
- drawing & label lines must be done w rly sharp pencil
- should take up at least 1/2 the page
- lines need to be clear & continuous & no shading/colouring
- ensure proportions are correct
- label all diff features you’ve shown - writing words in pencil/pen
- rule label lines (in pencil) - don’t let label lines cross e/o & don’t write on them
- ensure label lines touch part u r labelling
Steps for preparing microscope slides?
- pipette small drop of water onto centre of slide
- use tweezers to place a thin section of your specimen on top of the water drop aka ‘temporary/wet mount’ (specimen needs to let light through to be able to see it clearly)
- Add a. drop of a stain. (used to highlight objects in a cell)
- add the cover slip (protects the specimen) - stand slip upright on the slide, next to the water droplet -> carefully tilt and lower it so it covers the specimen (no air bubbles under there - obstruct view of the specimen)
