Microscopes Flashcards
What are the 3 types of microscopes
Optical microscopes
Transmission electron microscope
Scanning electron microscope
Define magnification
How many times larger the image is compared to the object
Define resolution
The ability to distinguish between 2 objects that are close together- higher resolution means more detail
How is the resolution of an optical microscope determined
By the wavelength of light
How is the resolution of both an transmission and scanning electron microscope determined
The wavelength of the beam of electrons
Why does electron microscopes have a higher resolution then optical microscopes
The wavelength of beam of electrons is much shorter so they have a higher resolution so the distance between the 2 objects is smaller
What is the equation of magnification
Image size/actual size
Conversation of units
M.
X1000 /1000
MM.
X1000 /1000
uM.
X1000 /1000
NM.
How do u convert mm to cm
/10
What is an eyepiece graticule used for
To measure the size of objects viewing under the microscope
What is cell fractionation
To isolate organelle so they can be studied
What do you do before the cell fractionation process
- separate cell organelles by cell fractionation
-solution must be kept in a cold,isotonic,buffered solution
In cell fractionation why does the solution have to be cold
To reduce enzyme activity as when cell breaks enzymes are released
This may damage organelles
In cell fractionation why does the solution have to be isotonic
So there is no osmosis ad it must have the same water potential so organelles don’t shrivel shrink and burst
In cell fractionation why does the solution have to be buffered
So PH is constant and dosnt denature enzymes and damage organelles
Describe the process of cell fractionisation- 1st step homogenisation
Homogenisation
- the cell must be homogenised using a blender breaking open cells to release contents / organelle’s
-place in cold,buffered,isotonic solution
-filter homogenate to remove large debris
What is the second process of cell fractionation and explain
Ultracentrifugation
- centrifuge homogenate in a tube at a low speed
● Remove pellet of heaviest organelle and respin supernatant
at a higher speed
● Repeat at increasing speeds until separated out, each time the
pellet is made of lighter organelles
What is the order of density’s in centrifugation stage of ultracentrifugation in cell fractionation from most dense to least dense
- Nuclei
- Chloroplast ( if using plant tissue)
- Mitochondria
- Lysosomes
- Endoplasmic reticulum
6.ribosomes
what are the principles of an optical microscope
Light focused using glass lenses
Light passes through specimen, different structures absorb different amounts & wavelengths
Generates a 2D image of a cross-section
Low resolution due to long wavelength of light
Can’t see internal structure of organelles or ribosomes
Specimen = thin
Low magnification (x 1500) Can view living oranisms
Simple preparation
Show colour
What are the principles of a transmission electron microscope
Electrons focused using electromagnets
Electrons pass through specimen, denser parts absorb more and appear darker
Generates a 2D image of a cross-section
Very high resolution due to short wavelength of electrons
Can see internal structures of organelles and ribosomes
Specimen = very thin
High magnification (x 1,000,000)
Can only view dead specimens as uses a vacuum
Complex preparation so artefacts often present
Does not show colour
Expensive
What are the principles of scanning electron microscope
Electrons focused using electromagnets
Electrons deflected / bounce off specimen surface
Generates a 3D image of surface
High resolution due to short wavelength of electrons
Can’t see internal structures Specimen does not need to be thin
High magnification (x 1,000,000)
Can only view dead specimens as uses a vacuum Complex preparation so artefacts often present Does not show colour
