Cell structure

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AS Biology
Cell Structure


• Magnification o The number of times an image is greater in
size than the object.
o Increases the ability to see details


• Resolution o The ability to distinguish two objects as separate
from each other.
o Allows details to be seen with more clarity o Determined

by the wavelength of light or electron beam



State the resolution and magnification that can be achieved by a
light microscope, a transmission electron microscope and a
scanning electron microscope.



• Light Microscope o Uses light o
Light passes through thin
specimen sample
o Sample
 Living or non-living o
Low magnification = x1,500
o Low resolution = 200µm
(half the λ of visible light)


AS Biology compiled by Sumaira Naseer

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o Stains - Dyes  Iodine

 methyl blue
 acetic orcein o Easy and cheap to create samples o
Easy and cheap to setup




• Transmission Electron Microscope (TEM) o Uses a beam of
electrons which pass through
the sample
o High magnification =
x500,000 o High resolution
= 0.1nm (The λ of electron
beam). o Sample
 Non-living o Creates a
2D image o Contrast is
created by structures of
different densities.
 Dense structures absorb more electrons and sop
appear darker
o Stains
 salts of heavy metals o Difficult and expensive to
create samples.
o Difficult and expensive to setup and use.




AS Biology compiled by Sumaira Naseer

, 3




• Scanning Electron Microscope
(SEM) o Uses a beam of electrons
which bounce off the surface of
the specimen.
o High magnification =
x100,000 o High resolution
= 0.1nm (The λ of electron
beam). o Sample
 Non-living o Creates a
3D image of the surface o
Stains
 salts of heavy metals o Difficult and expensive to
create samples.
o Difficult and expensive to setup and use.




AS Biology compiled by Sumaira Naseer