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microscopy (preparing microscope slides (step three: add a drop of a stain…
microscopy
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cell fractionation
homogenisation
its can be done in different ways: by vibrating the cells or by grinding them up in a blender. this breaks up the plasma membrane and releases the organelles into solution.
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filteration
filtered through a gauze to separate large cell debris and tissue debris., like connective tissue, from the organelles. the organelles are much smaller than the debris, so they pass through the gauze.
ultracentrifugation
- the call fragments are poured into a tube. the tube is put into a centrifuge and is spun at a low speed. the heaviest organelles, like nuclei, drop to the bottom of the tube by the centrifuge. they form a thick sediment at the bottom of the tube.
- the supernatant is drained off and poured into another tube. it is then span again at a high speed. the heaviest organelle drops to the bottom of the tube. the supernatant is drained off again and spun again.
- this process is repeated at higher speeds untill all the organelles are separated out. each time the pellet at the bottom of the tube is made up of a lighter and lighter organelle.
the order of heaviest to lightest organelles: neclei, mitochondria, lysosomes, ER, ribosomes. in plant cells the chloroplasts came after the nuclei.
resolution
resolution is how detailed the image is. its how well a microscope distinguishes between two points that are close together.
if a microscope lens cant separate two objects, then increasing the magnification wont help.
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types of microscopes
optical microscopes
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you cant use them if the organelle is smaller than 0.2 micrometres. this includes ribosomes, ER and lysosomes.
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electron microscopes
they use electrons to form an image. they have a high resolution meaning they can see organelles in a lot of detail.
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TEMs
TEMs use electronmagnets to focus a beam of electrons, which is then transmitted through the specimen. denser parts of the specimen absorb more electrons, which makes them look darker on the image you end up with.
ADVANTAGES: give high resolution images, so shows small objects.
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SEMs
they scan a bean of electrons across the specimen. this knocks off electron from the specimen, which are gathered in a cathode ray tube to form an image. the images you end up with show the surface of the specimen and they can be 3D
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