Electron microscope

Difference between

magnification &

resolution

• Magnification → how many times bigger the image is compared to the real object.

‣ Resolution → the minimum distance apart that two objects can be in order for them to be distinguished as separate objects.

Magnification formula

Microscopes: comparison

• Optical microscope.

‣ Ultrastructure not visible.

‣ Image is coloured.

• Scanning electron microscope.

‣ 3D image.

‣ Shows surface view.

‣ Transmission electron microscope.

‣ 2D image.

‣ Organelles (mitochondria) are visible.

‣ High magnification.

‣ High resolution.

Optical microscopes

Use light to observe whole cells / tissues.

‣ Use lenses to focus.

‣ Advantages:

‣ Can be used to view living cells.

‣ Natural colour of sample / colour of stain can be seen.

‣ Vacuum not required.

‣ Disadvantages:

‣ Lower resolution than electron microscopes → cannot

be used to see the ultrastructure of a cell because the

wavelength of light is not short enough (the only

organelle that can be seen is the nucleus).

Scanning electron

microscope (SEM)

Uses electrons.

‣ Use electromagnets to focus.

‣ Electrons are scattered by the surface based on the contours of the surface of the specimen.

‣ Advantages:

‣ 3D image.

‣ Shows surface view.

‣ Can be used on thick specimens.

‣ Disadvantages:

‣ Cannot be used on living tissue as whole system must be in a vacuum.

‣ Equipment is expensive.

‣ Lower resolution than TEM.

Transmission electron microscope (TEM)

Uses electrons & focuses using electromagnets.

‣ Advantages:

‣ High resolution images so can see the ultrastructure of a cell.

‣ Disadvantages:

‣ Produces 2D images.

‣ Can only be used on thin specimens.

‣ Cannot be used on living tissue as whole system must be in a vacuum.

‣ Equipment is expensive.

‣ Images are black and white.

‣ Complex preparation/staining procedure.