Comprehensive and in-depth notes on the biological aspects of this chapter, using specification points as headings to ensure that all required material is included- and no irrelevant content (like many of the textbooks). Created and used by an A-Level Biology student for the NEW SPECIFICATION from ...
(a) The use of microscopy to observe and investigate different types of cell and cell structure in a
range of eukaryotic organisms. (To include an appreciation of the images produced by a range
of microscopes: light microscope, transmission electron microscope, scanning electron
microscope and laser scanning confocal microscope.)
Light Microscope
• Pass light through the sample material
• Much lower resolution and magnification than that of electron microscopes
• Maximum resolution of about 0.2 micrometers
• Maximum magnification about x1500
• Easy to see individual cells and larger intracellular structures; like cell walls, nuclei, chloroplasts
and vacuoles
• The internal structure of organelles cannot be seen however
Electron Microscopes:
Use electrons instead of light to pass through specimen
Transmission Electron Microscope (TEM)
• Focused bean of electrons are passed through the sample material
• Produces 2D images
• Denser parts of the specimen absorb more electrons and so make them look darker on the
electron micrograph
• Very high resolution images
• Can be used to look at the internal structure of organelle
Scanning Electron Microscope (SEM)
• Electrons are bounced off of the sample material and collected
• Gives a 3D image of the structure
• Knocks off electrons on the sample which are then collected to make the micrograph
• Have a lower resolution than TEM’s.
Laser Scanning Confocal Microscopes
• Use laser beams to scan a specimen tagged with florescent dyes
• A splitter, splits a beam of light over the specimen and when the laser hits the dyes it emits
fluorescent light
• Florescent light is focused into a pinhole onto a detector which then generates an image
• Used to look at objects at different depth in thick specimens
• Multiple images can be taken to generate a 3D image
Instrument Maximum Magnification Maximum Resolution
Light Microscope x1 500 200nm
Transmission electron
x500 000 0.2nm
microscope
Scanning Electron Microscope x100 000 10nm
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