Studying Cells Flashcards
(20 cards)
Resolution
Ability to distinguish between two points
Magnification
How many times larger an image is compared to an object
How an optical microscope works
Light passes through a specimen
focused through glass lenses which can project a magnified image.
Max resolution and magnification of optical microscopes
Resolution = 0.2 micrometers
Magnification = 1500x (useful)
Conditions required for viewing slides under an optical microscope
Thin / single layer of cells
Stain (potassium iodide )
Preparing a temporary mount
Pippette a drop of water (keeps specimen flat)
Use tweezers to place a thin layer of tissue cell,
Add a drop of stain
Use mounting needle to lower cover slip
Advantages of optical microscopes
Can see living specimen
Can view specimen in colour
Slides are quicker to prepare
Disadvantages of optical microscopes
Lower resolution
Can’t view smaller organelles in detail
Lower magnification
How does a transmission electron microscope work?
Beams of electrons pass through the specimen
Electronic pass through less dense parts more easily
Scattered electrons are captured on a photographic plate
Darker parts = more dense
Magnification and resolution of TEM
Magnification = x 250 000
Resolution = 2 nanometers
How does a scanning election microscope work?
Specimen coated in a layer of metal
Electromagnet focuses beam of elections
Electrons bounce of surface on to photographic plate
Magnification and resolution of SEM
Magnification = x100 000
Resolution = 3-20 manometers
Advantages of electron microscopes
Higher resolution
Higher magnification
Can produce 3D images (sem)
Why do electron microscopes have a higher resolution than optical microscopes?
Electron beams have a shorter wavelength than light
Disadvantages of election microscopes
Must be in a vacuum
Can’t new living specimen
Not in colour
Complex staining process
Must be a very thin specimen (tem)
Comparisons between TEM and SEM
SEM has a lower resolving power than TEM
TEM produces 2D images but SEM produces 3D images
Cell fractionation
Process where cells are broken up and the different organelles they contain are separated
Why is tissue placed in cold, isotonic, buffered solutions during homogenation?
Cold = reduce/ stop enzyme activity
Isotonic = prevents osmosis
Buttered = controlled pH prevents enzyme denature and organelle damage
Steps of cell fractionation and ultracentrifugation
Tissue is minced and placed in cold, isotonic, buffered solution
Homogeniser grinds into smaller pieces (releases organelles)
Homogenate is filtered (removes whole cells and large debus)
Suspension of homogenate is centrifuged in a test tube
Centrifuge at a lower speed so larger fragments (nucleus) collect at the bottom and smaller fragments suspended in supernatant
Sediment pellet removed and rest of supernatant is re-spun at higher speed
Mitochondora/chloroplast will collect next
Differential centrifugation
Process involved in centrifuging at different speeds
