2 - Methods of studying cells Flashcards
(15 cards)
Describe magnification
How many times larger is compared to actual size of objects
Describe resolution
Ability to distinguish two objects that are close together
Principles of optical microscopes
- Beam of light focused on lens to create an image
- Longer wavelength of light so lower resolution
Limitation of optical microscope
- Lower resolution because light has a longer wavelength
- Lower magnification
Principles of SEM and TEM
- Electrons pass through specimen
- Denser parts absorb more electrons
- Denser parts appear darker
- Electrons have short wavelength so have high resolution
Limitation of TEM (4)
- Cant look at living material
- Must be in a vacuum
- Specimen must be thin
- Artefacts present
- Complex staining method
- Black and white images
Advantages of SEM (3)
- Sections do not need to be prepared
- Shows surface of specimen
- 3D images
Advantages of optical microscopes
- Colour images
- View living samples
What must the solution be in cell fractionation?
Cold, isotonic, buffered
Why must solution be cold?
Reduce enzyme activity, enzymes could damage organelles
Why must the solution be isotonic?
Same water potential as the solution to prevent osmosis which could cause cells to shrivel or burst
Why must the solution be buffered?
Buffers change in pH to prevent damage to organelles
What are the two steps of cell fractionation?
1) Homogenisation
2) Ultracentrifugation
What is cell homogenisation?
Cells must be broken open with a blended in a cold, isotonic and buffered solution. Filter to remove large debris.
What is ultracentrifugation?
Centrifuge spins at high speeds and forces out pellets with the most dense organelles at the bottom of the cells.
Process repeated at higher speeds removing the liquid each time leaving behind the pellet of isolated organelle.
