- Microscopes are instruments that produce a magnified image of an object.
- A convex glass lens acts as magnifying glass, they are more effective if in pairs like a compound microscope.
- Long wavelengths of light means a light microscope can distinguish between two objects if they are 0.2μm or further.
- This can be overcome by using beams of electrons rather than beams of light
- With shorter wavelengths, the beam of electrons in the electron microscope can distinguish between two objects only 0.1nm apart
- material under a microscope = object
- appearance of material when viewed under microscope = image
- Magnification = (size of image) / (size of real object)
- Size of real object = size of image/ magnification
- Kilometer (km) =103
- Metre (m) = 1
- Millimetre (mm) = 10-3
- Micrometre (μm) =10-6
- Nanometre (nm) =10-9
- Resolution or resolving power of microscope is minimum distance apart that two objects can be in order for them to appear as separate items
- Resolving power depends on wavelength or form of radiation used
- In light microscope, it is about 0.2μm
- Means that any objects which are 0.2μm or more apart will be seen separately but any objects closer than 0.2μm will appear as single item
- Greater resolution means greater clarity, this image produced is clearer and more precise
- increasing magnification increases size of an image but doesn’t always increase resolution
- every microscope has limit of resolution
- up to this point increasing the magnification will not do this.
- Object while appearing larger will be more blurred
- Process where cells are broken up and the different organelles they contain are seperated.
- Before it can take place it must be in
- Cold - to reduce enzyme activity that might break down the organelles
- Isotonic - to prevent organelles bursting or shrinking due to osmotic gain or loss of water
- Buffered - so pH doesn't fluctuate as it could alter structure of the organelles or affect functioning of enzymes
- Homogenation - cells broken up by homogeniser (blender) to release organelles from cells. Fluid left is homogenate which is filtered to remove any complete cells and large pieces of debris
- Ultracentrifugation - process by which fragments in filtered homogenate are separate in machine called centrifuge = spins tubes of homogenate at very high speeds in order create a centrifugal force
- Filtrate is placed in a centrifuge and spun at slow speed
- Heaviest organelle sinks to form a pellet and fluid left is supernatant
- Supernatant is removed and transferred then spun again at a faster speed than before.
- The next heaviest organelles, mitochondria, are forced to the bottom of the tube
- process is continued in this way so that at each increase in speed, next heaviest organelle is sedimented and separated out.
- Results: Nuclei 1st at 1,000 revolutions per min. Then mitochondria at 3,500 revolutions per min. Then Lysosomes at 16,500 revolutions per min
The electron microscope
- Light microscopes have poor resolutions as result of relative;y long wavelength of light
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