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Cell Fractionation
This is a method of getting the organelles out of cells in order to study them or
use them under a microscope.
Before cell fractionation begins tissue is put in a test tube with certain
Cold ­ reduce enzyme action that could break down organelles
Isotonic ­ prevent organelles bursting or shrinking as a result of osmosis
Buffered ­ to maintain constant pH
This is the first step where cells are broken up by a homogeniser(blender) to
release organelles from cell. The homogenate is then filtered to remove
complete cells and large pieces.
The next step is to put the filtered homogenate into an ultracentrifuge, which
spins the tubes at very high temperatures. When this happens the heaviest
organelles are forced to the bottom of the tube forming a sediment leaving a
fluid on top the supernatant. You remove the sediment and you will have the
heaviest organelles such as nuclei, and then you put the supernatant back in
the centrifuge at a higher speed in order to get the next heaviest organelle to
form a sediment. The order in which the organelles is collected decreases with…read more

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Investigating structure of
Material under microscope is referred to as object. The
appearance of this material when viewed under
microscope is the image. Magnification of an object is
how many times bigger the image is compared to the
Magnification = Image
This is the minimum distance apart that two objects can
be in order for them to appear as seperate items.
Increasing magnification will increase size of image
but not always resolution.…read more

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Electron Microscope
Electron microscopes use electrons to form the image and you
look at a picture of the specimen not the specimen itself.
They have a higher resolution than a light microscope
because electrons have a shorter wavelength. Because the
electrons are negatively charged beams can be focused using
Transmission Electron Microscope
Electron gun produces a beam of electrons which are focused
onto specimen by electromagnet. Beam passes through a
thin section of specimen. Parts of specimen absorb electrons
and appear dark other allow electrons to go through and
appear light. This black and white image is produced on a
screen and is called a photomicrograph.
Scanning Electron Microscope
SEM directs a beam of electrons on to surface from above
rather than penetrating it from below. Beam is passed back
and forth across specimen . Electrons are scattered and this
generates a pattern according to the contours of specimen
surface. A 3-D image is built by computer analysis of the
pattern of scattered electrons.…read more

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Electron Microscope
Differences and similarities between TEM and
Transmission Scanning
Electrons penetrate so specimen must Electrons directed onto surface
be thin. specimen can be thick.
Electrons pass through parts of Beam passed backwards & forwards
specimen giving light and dark parts. across specimen, scattering electrons
depending on its contours.
Black and White image produced 3D image built by computer
called photomicrograph
Higher resolving power Lower resolving power
Vacuum so living specimens cant be Vacuum so living specimens cant be
observed observed.
Complex staining causes artefacts Complex staining causes artefacts
(change in specimen) (change in specimen)…read more

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Contains genetic material and controls
cell's activities. It has a number of
Nuclear Envelope ­ double
membrane that surrounds nucleus. It
joins with endoplasmic reticulum.
Controls entry and exit of materials
in and out of nucleus.
Nuclear Pores ­ allow passage of
large molecules such as messenger
RNA out of nucleus
Chromatin ­ is DNA found within
nucleus. It is the extended form taken
by chromosomes during interphase.
Nucleolus ­ small spherical body
within nucleus that manufactures…read more

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