Cells and cell techniques, organelles biol1

what u see is what u get.

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Microscopes ­ depends on magnification and resolving power.
Magnification ­ `the number of times bigger the image appears compared to its actual size'
Resolving power (resolution) ­ `the minimum distance between 2 objects at which they can be seen as
Compound light/optical microscope ­ Wavelength of visible light determines the resolving power and
therefore the maximum effective magnification. It is powerful enough to see cells and larger organelles but not
individual bacteria.
Magnification of eyepiece lens x magnification of objective lens
E.g. resolving power is 0.2 = 2 objects closer together than 0.2um will appear as one object
Electron microscope ­ uses beam of electrons, focused by electromagnets instead of light. It is varied by
changing the strength of electromagnets electron beams have a smaller wavelength than light rays meaning
there is a higher resolving power.
Specimen ­ must be prepared inside a chamber in the electromagnet which is sealed and the air is sucked
out to produce a vacuum as electrons otherwise will be deflected by molecules in air. Electromagnets focus a
beam of electrons that either pass through the specimen or reflect it into a viewing screen.
Transmission electron microscopes (TEM) work as the principle of the beam of electrons is transmitted
through the specimen. The specimen must be very thin and stained using an electrondense substance such
as heavy metal salts. These will deflect electrons in the beam and a pattern is produced that is then converted
into an image
Scanning electron microscopes (SEM) ­ study 3D objects, sections not required as the SEM record the
electrons that are reflected off the surface of the object rather than passing through it.
Lower resolution than TEM Higher resolution than SEM
Does not require thin sections to be cut Requires thin sections
Can have 3D images No 3D images
Only shows surface of object Allows internal cell details to be seen
Radiation source Light Electrons
Method of focus Lenses Electromagnets
Maximum resolution 0.2 um 1nm
Maximum magnification x1500 X500000
Advantages Coloured images Higher resolution as
Living specimens seen electron beam wavelength
Preparation of specimens shorter than that of light
is simple Higher magnification
Fine detail can be seen
Limitations Lower resolution limited by TEM require very thin
wavelength of light specimen
Lower magnification Black and white images
Vacuum is essential so only
dead specimens may be
Cell structure and function all cells contain a plasma membrane enclosing cell contents, cytoplasm, genetic
material that is made of DNA.

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Prokaryotes ­ simple cells e.g. bacteria
Eukaryotes ­ cells found in plants and animals that have membranebound organelles
Organelle ­ small cellular structure that has a specific function
Viruses are noncellular/akaryotic and cannot carry out metabolic processes.
Metabolism ­ all the chemical reactions in cells e.g. respiration
Prokaryotes ­ Genetic material is not enclosed in a nuclear envelope, do not contain any membrane bound
Genetic material Circular loop of DNA not Carries genetic information,
associated with proteins.…read more

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Smooth Endoplasmic Reticulum Membranes for, a series of tubes Synthesis lipids and transport of
(cisternae) in the cytoplasm of the lipids
cell. No ribosomes attached
Golgi Body Stack of flattened sacs, each Packages and processes
surrounded by a membrane.…read more


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