Cells and Movement In and Out of Them

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  • Created on: 25-01-15 19:56
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Cells and movement in and out of them
We use microscopes to magnify the image of an object that is not visible to the naked eye. An
object is a material you put under a microscope and the image is the appearance of this object
when viewed through the microscope. The magnification of an object is how many times bigger
the image is compared to the object. It is shown by:
magnification = size of image
size of object
This equation can be rearranged to calculate the size of an object from the image and
magnification. Ensure that the units of length are the same for both the object and the image.
Metre (m) 1
Millimetre (mm) 10-3
Micrometre 10-6
Nanometre (nm) 10-9
The resolution or resolving power of a microscope is the minimum distance apart that two objects
can be in order for them to appear a separate items. Resolving power depends on the wavelength
or the form of radiation used. The resolution of a light microscope is about 0.2µm.
Increasing the magnification will increase the size of an image but does not always increase the
resolution. Every microscope has a limit of resolution and beyond this point the image will just
become blurred when the magnification is increased.
Cell fractionation
Biologists need to obtain large numbers of isolated organelles to study their structure and
function. Cell fractionation is a process where cells are broken up and the different organelles they
contain are separated out.
Before cell fractionation can begin the tissue is placed in a cold, isotonic, buffered solution. The
solution is cold to reduce enzyme activity that might break down organelles, isotonic (a solution
that has the same water potential as the original tissue) to prevent the organelles bursting or
shrinking as a result of osmotic gain or loss of water and buffered to resist any changes in pH that
could be destructive.
There are two stages to cell fractionation:
Cells are broken up by a homogeniser (blender). This releases the organelles from the cell. The
resultant fluid (known as homogenate) is then filtered to remove any complete cells and large
pieces of debris.

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This is the process by which the fragments in the filtered homogenate are separated in an
ultracentrifuge. This machine spinds tubes of homogenate at a high speed in order to create a
centrifugal force. For animal cells, the process is as follows:
The tube of filtrate is placed in the ultracentrifuge and spun at a low speed, forcing the
heaviest organelles (nuclei) to the bottom of the tube where they form a thin sediment or
pellet.…read more

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A complex `staining' process is required and even then the image is in black and white.
The specimen must be extremely thin
The image may contain artefacts (things that result from the way the specimen is
prepared, not what you're observing) however improvements in technique can eliminate
most of these.
The scanning electron microscope (SEM):
All the limitations of the TEM apply to the SEM except that the specimen does not need to be as
thin as the electrons do not penetrate it.…read more

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The enzymes involved in respiration are found in the
Mitochondria are responsible for the production of the energy-carrier molecule ATP, from
carbohydrates. Because of this, the number of mitochondria increases in cells that have a high
level of metabolic activity and therefore need a plentiful supply of ATP. Epithlial cells are
metabolically active since they use a lot of energy in the process of absorbing substances from the
intestines via active transport.…read more

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The functions of lysosomes are to:
Break down material ingested by phagocytic cells, such as white blood cells
Release enzymes to the outside of the cell (exocytosis) to destroy material around the cell
Digest worn out organelles so that the useful chemicals they are made of can be re-used
Completely break down cells after they have dies (autolysis)
These are small cytoplasmic granules found in all cells. They may occur in the cytoplasm or be
associated with the RER.…read more

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Rough Extensive Collects, stores,
endoplasmic membrane system packages and
reticulum with ribosomes transports the
attached. proteins made on the
Connected to ribosomes.
nuclear membrane.
Smooth Membrane system Systhesis of lipids and
endoplasmic with no ribosomes some steroids.
reticulum attached. Occurs in
small patches in
the cytoplasm.
Golgi Stack of flattened Receives vesicles from
apparatus membrane discs rough ER. Appears to
found free in the synthesise/modify
cytoplasm, close to chemicals before their
the rough ER. secretion from the
Varies in size. cell.…read more

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As the glycerol molecule in all triglycerides is the same, the differences in the properties of the
different fats comes from variations in the fatty acids.
Phospholipids are similar to lipids except that one of the fatty acid molecules has been replaced by
a phosphate molecule. Phosphate molecules (head) are hydrophilic where fatty acid molecules
(tail) are hydrophobic. Phospholipid molecules are therefore polar.
Emulsion test for lipids:
1. Add 2cm3 of the sample being tested to a dry, grease-free test tube
2.…read more

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There are a number of factors that affect the rate at which diffusion takes place:
Concentration gradient ­ the greater the difference in concentration of the molecules or
ions, the faster the rate of diffusion
Area over which diffusion takes place ­ the larger the area of an exchange surface, the
faster the rate of diffusion
Thickness of an exchange surface ­ the thinner an exchange surface, the faster the rate of
Diffusion is proportional to:
surface area × difference in concentration
length…read more

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The highest value for water potential, that of pure water, is zero, and so all other values are
Animal cells contain a variety of solutes dissolved in their cytoplasm. To prevent water moving in
or out via osmosis, animal cells are normally bathed in a liquid which has the same water potential
e.g. red blood cells are surrounded by blood plasma.…read more

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Active transport
Metabolic energy in the form of ATP is needed
Carrier protein molecules which act as `pumps' are involved
Selective process
Direct active transport of a single molecule or ion:
Carrier proteins span the cell surface membrane and accept the molecules/ions to be
transported on one side of it.
Molecules/ions bind to receptors on the channels of the carrier protein.
On the inside of the cell, ATP binds to the protein, causing it to split into ADP and a
phosphate molecule.…read more


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