Module 1 - Cells

Cells can be prepared by;

Staining - Coloured stains are chemicals that bind to chemicals on or in the specimen. They allow the specimen to be seen. Some stains bind to specific cell structures.

Sectioning - Specimens embedded in wax. Thin sections are then cut without distorting structure. Particularly useful for making sections of soft tissue e.g. brain.

Actual size = Image size/Magnification. um - micrometre, nm - nanometre

e.g.

Diameter = 5 um

Measure diameter - 25mm

Multiply by 1000 (um) - 25000um

Divide diameter by actual size 25000/5000 -Magnification = 5000x-

Transmission electron microscope (TEM)

• Electron beam passes through a very thin prepared sample.Produces 2D image.
• Electrons pass through the denser parts of sample less easily, giving contrast.
• Magnification possible is x500,000.

Scanning electron microscope (SEM)

• Electron beam directed onto a sample, not through. They 'bounce off' the sample.
• Final 3D view of surface of sample produced.
• Magnification possible is x100,000.

Advantages & Limitations of electron microscope.

• Adv - Resolution is 2000x more than in the light microscope.
• Adv - Therefore can be used to produce detailed images of structure inside cells.
• Dis adv - Have to be in a vacuum as electron beams deflected by molecules in air.
• Dis adv - Preparation & use of electron microscope require high skill and training.