Chapter 3 Cell Structure Flashcards
What are microscopes?
An instrument that produces a magnified image of an object
What is the definition of magnification?
The degree to which size of an image is larger than the object itself
What is the definition of resolution?
The minimum distance apart that two objects can be in order for them to appear as separate items
What is the equation for magnification?
Magnification = Size of image/Size of real object
What is cell fractionation?
The process where cells are broken up + the different organelles they contain are separated out
Where is the tissue placed in before Cell fractionation and why?
A cold, buffered solution
Cold - Reduce enzyme activity
Buffered - Ph won’t fluctuate
Same H2O potential tissue - Prevents organelles from bursting or shrinking
Describe the first stage of Cell fractionation
Homogenation
1) Cells are broken up by a homogenizer (blender), releases organelles from the cell
2) Resultant fluid (homogenase) is filtered to remove complete cells + large pieces of debris
Describe the second stage of Cell fractionation
Ultracentrifugation
Fragments in homogeniser are separated in a centrifuge - This spins tubes of homogenase at very high speed in order to create a centrifugal speed
1) Tube of filtrate placed in centrifuge + spun at slow speed
2) Heaviest organelles (nuclei) forced at the bottom of the tube and form thin sediment or pellet
3) Fluid at the top of the tube (supernatural) is removed, leaving sediment nuclei
4) The supernatant is transferred to another tube + spun at a faster speed
What are the advantages of the electron microscope?
The electron beam has a short wavelength
High resolving power
Electrons negatively changed, beams focused using electromagnets
What condition is needed to be created in order for the electron microscope to work efficiently?
A vacuum has to be created within a chamber of the EM in order to work efficiently
What resolution does the Electron Microscope work at?
o.1nm = 2000x more than LM
What is the Transmission Electron Microscope?
Consists of an electron gun that produces a beam of electrons that is focused onto the specimen by a condenser electromagnet (2D image)
How does a Transmission Electron Microscope work?
1) Beam passes through thin section of specimen
2) Parts of specimen absords electrons therefore it appears dark
3) Other parts of specimen allow electrons pass through + appear bright
4) Image produced on screen, photogrpahed to give photomicrograph
What are the limitations of a Transmission Electron Microscope?
- The whole system must be in a vacuum, therefore, no living specimens can be used
- Complete staining required
- The specimen must be extremely thin
- Image may contain artifacts
- High beam energy required, may destroy the specimen
Describe how the Scanning Electron Microscope works?
1) Directs beams electrons to surface of specimen from above
2) Beam passed back and forth across portion specimen in regular pattern
3) Electrons scattered by specimen + pattern of scattering depends on specimen surface
4) Build 3D-image by computer analysis
SEM has a lower reducing power than TEM
20nm 10x better than LM
What are the limitations of the scanning electron microscope?
- The whole system must be in a vacuum, therefore, no living specimens can be used
- Complete staining required
- Image may contain artifacts
- High beam energy required, may destroy the specimen
How can we measure the size of an object using a light microscope?
By using an eyepiece graticule
