Module 2: Cell Structure
Microscopes
Magnification = the number of times larger an image appears, compared with the size of
the specimen
1000 micrometres = 1 mm
Resolution = the ability to see two objects that are close together as separate objects
In light microscopes the resolution is limited by the wavelength of light
Electron microscopes have a much higher resolution than light microscopes because
electrons have a smaller wavelength than visible light
Microscopes:
1. Optical (/Light) Microscopes
2. Electron Microscope
Electron Microscope Light Microscope
Large and installation mean it Small and easy to carry
can’t be moved No vacuum needed
Vacuum needed Easy sample preparation
Complicated sample preparation Up to x2000 magnification
Over x500,000 magnification Resolution 200nm
Resolution 0.5mm Specimens can be living or dead
Specimens are dead
,Optical Microscopes:
Photomicrograph = photograph of an image seen using an optical microscope
Light or optical microscopes use light to form an image
The max resolution of a light microscope is around 0.2 micrometres, meaning the
maximum magnification of optical microscopes is about x1500, in some types x2000
Light microscopes can only be used to observe large structures - entire cells, nuclei,
mitochondria, chloroplasts
ADV DISADV
They are small and relatively Magnifies specimens up to
cheap x2000 only
Specimen preparation can be Resolution limited up to 200
straightforward enough to nm (0.2 um)
perform in a school laboratory
They can be used to produce
colour images
They allow the observation of
living specimens
Electron Microscopes:
Electron Micrograph = photograph of an image using an electron microscope
Electron microscopes use electrons to form an image
Electron microscopes have a maximum resolution of around 0.0002 micrometres or
0.2 nm, meaning the maximum magnification ranges from x 1,000, 000 up to many
millions
Electron microscopes can be used to observe viruses and small structures inside
cells - cell membranes, ribosomes, the endoplasmic reticulum, lysosomes
Metallic salt stains are used on the specimen to make cells more visible and to
increase contrast between different parts of them.
ADV DISADV
High resolution ( up to 0.2 Large and expensive
nm)
Specimens must be prepared
High magnification using a highly complex
process
Specimens must be viewed
in a vacuum, meaning that
live specimens cannot be
, observed
Images are always black and
white, though they can be
artificially coloured during
processing
Need a great deal of skill and
training to use
There are two types of electron microscope :
1. Transmission electron microscopes (TEMs) - 1930s
2. Scanning electron microscopes (SEMs) - 1960s
Transmission Electron Microscope:
TEMs use electromagnets to transmit a beam of electron through a specimen
Denser parts of the specimen absorb more electrons, meaning that denser parts
appear darker on the final image
TEMs produce images that are:
o Higher resolution images than SEMs
o Higher magnification than SEMs
o Allow the internal structure within cells and within organelles to be seen
o Show 2D images
Scanning Electron Microscope:
The SEM is designed for the study of the surfaces of solid objects such as insect and
pollen grains, so SEMs pass a beam of electrons across the surface of a specimen
and then detect the rate of which the electrons bounce back
SEMs specimen samples are usually thicker, which also prevent electrons from
passing through
A metal coat is applied to SEM samples to improve resolution and preventing
samples from accumulating electrons charge when hit by the electron beam, causing
Microscopes
Magnification = the number of times larger an image appears, compared with the size of
the specimen
1000 micrometres = 1 mm
Resolution = the ability to see two objects that are close together as separate objects
In light microscopes the resolution is limited by the wavelength of light
Electron microscopes have a much higher resolution than light microscopes because
electrons have a smaller wavelength than visible light
Microscopes:
1. Optical (/Light) Microscopes
2. Electron Microscope
Electron Microscope Light Microscope
Large and installation mean it Small and easy to carry
can’t be moved No vacuum needed
Vacuum needed Easy sample preparation
Complicated sample preparation Up to x2000 magnification
Over x500,000 magnification Resolution 200nm
Resolution 0.5mm Specimens can be living or dead
Specimens are dead
,Optical Microscopes:
Photomicrograph = photograph of an image seen using an optical microscope
Light or optical microscopes use light to form an image
The max resolution of a light microscope is around 0.2 micrometres, meaning the
maximum magnification of optical microscopes is about x1500, in some types x2000
Light microscopes can only be used to observe large structures - entire cells, nuclei,
mitochondria, chloroplasts
ADV DISADV
They are small and relatively Magnifies specimens up to
cheap x2000 only
Specimen preparation can be Resolution limited up to 200
straightforward enough to nm (0.2 um)
perform in a school laboratory
They can be used to produce
colour images
They allow the observation of
living specimens
Electron Microscopes:
Electron Micrograph = photograph of an image using an electron microscope
Electron microscopes use electrons to form an image
Electron microscopes have a maximum resolution of around 0.0002 micrometres or
0.2 nm, meaning the maximum magnification ranges from x 1,000, 000 up to many
millions
Electron microscopes can be used to observe viruses and small structures inside
cells - cell membranes, ribosomes, the endoplasmic reticulum, lysosomes
Metallic salt stains are used on the specimen to make cells more visible and to
increase contrast between different parts of them.
ADV DISADV
High resolution ( up to 0.2 Large and expensive
nm)
Specimens must be prepared
High magnification using a highly complex
process
Specimens must be viewed
in a vacuum, meaning that
live specimens cannot be
, observed
Images are always black and
white, though they can be
artificially coloured during
processing
Need a great deal of skill and
training to use
There are two types of electron microscope :
1. Transmission electron microscopes (TEMs) - 1930s
2. Scanning electron microscopes (SEMs) - 1960s
Transmission Electron Microscope:
TEMs use electromagnets to transmit a beam of electron through a specimen
Denser parts of the specimen absorb more electrons, meaning that denser parts
appear darker on the final image
TEMs produce images that are:
o Higher resolution images than SEMs
o Higher magnification than SEMs
o Allow the internal structure within cells and within organelles to be seen
o Show 2D images
Scanning Electron Microscope:
The SEM is designed for the study of the surfaces of solid objects such as insect and
pollen grains, so SEMs pass a beam of electrons across the surface of a specimen
and then detect the rate of which the electrons bounce back
SEMs specimen samples are usually thicker, which also prevent electrons from
passing through
A metal coat is applied to SEM samples to improve resolution and preventing
samples from accumulating electrons charge when hit by the electron beam, causing
