Cell structure Flashcards
what are microscopes used for
to produce magnified images of objects
describe how light microscopes work
use visible light beam (wave length 400nm - 700nm) to produce a 2D photomicrograph
what’s the resolution in light microscopes and what are the limitations of this?
- 50-200nm
- ribosomes (20nm) aren’t distinguishable
what are the advantages of using light microscope
- cheap
- easy to use
- portable
- able to view living specimens
equation for total magnification
total magnification = objective lens magnification x eyepiece lens magnification
describe how laser scanning microscopes work
specimen is treated with a flourescent dye and a laser beam scans images point by point causing the dye to be seen
what are the advantages of using laser scanning microscopes
- high-resolution, high contrast computer image is formed from pixels
- depth selectivity allows the microscope to view specimens at different depths
what can laser scanning microscopes be used for
- **to look at an object at a certain depth within a cell **
- can be used to swiftly diagnose conditions
describe how electron microscopes work
- use a beam of electrons with a wavelength 0.004nm to produce much higher resolution images
what is a disadvantage of electron microscopes?
- samples must be placed in a vacuum so living organisms can’t be viewed
how are specimens prepared in TEMs ( transmission electron microscopes)
specimen dehydrated and stained
what role do electrons play in TEMs
pass through the specimen
what’s the product of TEMs
2D black and white micrograph
what’s the magnification and resolution of TEMs
- 500’000x magnification
- 0.5-1nm resolution
how are specimens prepared in SEMs ( transmission electron microscopes)
dead specimen placed in a vaccume and coated with metal film
what role do electrons play in SEMs
scan the surface of a specimen, bounce off and the refelected beam if viewed
what’s the product of SEMs
3D image formed, B+w but can have false colour added
what’s the magnification and resolution of SEMs
- 100,000x magnification
- 0.2nm resolution
why are specimens stained
allows the specimen to become visible, identify different organelles, and increase contrast
what’s differential staining
when different stains bind to specific structures in the cell
steps in specimen preparation
- dehydration
- embedded in wax, preventing distortion
- slicing into thin selections
name 4 stains
- acetic orcein
- eosin
- iodine in KI
- sudan black
what’s the function of acetic orcein
binds to DNA, stains chromosomes dark red in colour
what’s the function of eosin
stains the cytoplasm pink
what’s the function KI stain
stains cellulose yellow, starch grains blue-black
what are eyepiece graticules used for
to measure object sizes in eyepiece units (epu)
what are stage micrometer used for
used to calibrate the eyepiece graticule
how do you measure specimen size
- fit eyepiece (10x) and stage graticules focus with objective lens for a given magnification
- work out what length each epu represents. Stage graticule measures in microns
- measure object epu and multiply by this value
define magnification
the number of times larger an image appears compared to the real specimen
define resolution
the ability to distinguish two points that are close together clearly as two seperate entities