2.1.3 methods of studying cells Flashcards
what is magnification
number of times greater an image is than the size of the actual object
what is the equation for magnification
size of image/size of real object
what is resolution
minimum distance apart 2 objects which can be distinguished as separate objects
what are the three different types of microscope
- optical
- transmission electron microscope
- scanning electron microscope
how are microscopes focused
- optical = light is focused using glass lenses
- TEM and SEM = electrons focused using electromagnets
how do microscopes work
- optical = light passes through specimen, different structures absorb different amounts and wavelengths
- TEM = electrons pass through specimen, denser parts absorb more and appear darker
- SEM = electrons deflected off specimen surface
what type of image do microscopes create
- optical and TEM = generates 2D image of cross section
- SEM = generates 3D image of surface
what is the resolution of microscopes
- optical = low resolution due to long wavelength of light
- TEM = very high resolution due to short wavelength of electrons
- SEM = high resolution due to short wavelength of electrons
what structures can you see with microscopes
- optical and SEM = cant see internal structure of organelles or ribosomes
- TEM = can see internal structure and ribosomes
how does the specimen have to be when using a microscope
- optical = thin
- TEM = very thin
- SEM = doesnt need to be thin
what is the magnification of microscopes
- optical. = low magnification ( x1500 )
- TEM and SEM = high magnification ( x1,000,000 )
can you view living organisms with microscopes
- optical = yes
- TEM and SEM = can only view dead/dehydrated specimens as uses a vacuum
what is the preparation like to use a microscope
- optical = simple
- TEM and SEM = complex preparation so artefacts often present
can microscopes show colour
- optical = yes
- TEM and SEM = no
describe how to convert between different units
metres x1000, millimetres x1000, micrometer x1000, nanometer
describe how the size of an object viewed with an optical microscope can be measured
- line up eye piece graticule with stage micrometer
- calibrate eye piece graticule - use stage micrometer to calculate size of divisions on eye piece graticule
- take micrometer away and use graticule to measure how many divisions make up the object
- calculate size of object by multiplying number of divisions by size of division
- recalibrate eye piece graticule at different magnifications
what are the 4 steps of cell fractionation and ultracentrifugation used to separate cell components
- homogenisation
- place in cold isotonic buffered solution
- filter homogenate
- ultra centrifugation
what is the step of homogenisation
homogenise the tissue using a blender to disrupt the cell membrane, breaking open the cells and releasing organelles
why is the solution cold, isotonic and buffered
cold = to reduce enzyme activity so organelles are not broken down
isotonic = so water doesnt move in or out of organelle by osmosis so they dont burst
buffered = to keep pH constant so enzymes dont denature
what is the step of filtering the homogenate
removing large unwanted debris eg. whole cells or connective tissues
what is the step of ultracentrifugation
separates organelles in order of density/mass:
- centrifuge homogenate in a tube at high speed
- remove pellet of heaviest organelle and respin supernatant at higher speed
- repeat at increasing speeds until separated out, each time pellet made of lighter organelles
what is the order of organelle mass ( heaviest to lightest )
- nuclei
- chloroplasts/mitochondria
- lysosomes
- ER
- ribosomes
