3.1 Studying cells Flashcards
What is the equation for magnification?
Magnification = size of image/size of real object
Define resolution/resolving power
The minimum distance apart that two objects can be in order for them to appear as separate items
Define magnification
How many times bigger the image is when compared to the object
What is cell fractionation?
The process where cells are broken up and the different organelles they contain are separated out
What happens before cell fractionation and why?
Placed in cold, buffered, isotonic solution
Cold - reduced enzyme activity that might break down the organelles
Isotonic- same water potential as tissue to prevent organelles bursting or shrinking
Buffering - pH same - change could alter the structure of the organelles or affect the function of enzymes
What are the 2 stages of cell fractionation?
Homogenation
Ultracentrifugation
What happens during homogenation?
Cells broken up by a homogeniser which release the organelles
Homogenate filtered to remove any complete cells and large pieces of debris
What happens during ultracentrifugation?
- Tube of filtrate is placed in the centrifuge and spun at a slow speed
- Heaviest organelles, nuclei, forced to the bottom of the tube in the pellet
-Supernatant removed - Supernatant transferred and spun in the centrifuge at a faster speed
- Next heaviest, mitochondria, forced to the bottom –> process continues
Describe the disadvantages of a light microscope
Long wavelength of light so low resolution
Low magnification
Specimens must be thin so may not be representative and hard to do
Describe the advantages of a light microscope
Easier
Cheaper
‘True colour’
Could use live specimen
What is an artefact?
‘Mistake’
- Air bubble or clump of stain
How does a transmission electron microscope work?
A beam of electrons passes through a thin section of the specimen
Parts of this specimen absorb electrons and therefore appear dark
2D image
Describe the disadvantages of a TEM
- Must be in a vacuum so only dead specimens
- Complex staining system then the image in black and white
- Must be extremely thin
Why might a TEM not achieve its resolving power of 0.1nm?
Difficulties preparing the specimen
Higher energy electron beam required and this may destroy the specimen
