microscopes

advantages of optical microscopes

• can observe living cells

• simple sample prep

• inexpensive in comparison to electron microscopes

disadvantages of optical microscopes

• lower magnification

• lower resolution

• light has a longer wavelength than electrons, so lower resolution of light microscope

• can’t see smaller organelles such as ribosomes/lysosomes

magnification

how many times larger the image is compared to the actual object

resolution

the ability to distinguish between 2 separate points

how do transmission electron microscopes work

• beam of electrons passes through a very thin specimen

• denser areas absorb more electrons & appear darker, while less dense areas appear lighter

• produces a 2D, black & white image with extremely high resolution

uses of TEM

• studying the ultrastructure of cells (e.g. smaller structures like ribosomes)

• examining internal details of viruses and bacteria

how does a SEM (scanning electron microscope) work

• a beam of electrons is directed onto the surface of a specimen

• electrons are reflected off the surface and detected to produce a 3D image

• provides detailed surface structure rather than internal details

uses of SEM

• studying surface structures of cells, viruses, & tissues

• examining insects, pollen grains, & other surfaces in high detail

advantages of electron microscopes

• much higher magnification than light microscopes

• higher resolution so finer details can be seen

• can reveal details of smaller organelles (TEM) & 3D surface structures (SEM)

disadvantages of electron microscopes

• specimens must be dead since electron microscopes require a vacuum

• complex sample prep - very thin sections for TEM & coating with metals for SEM

• expensive - requires specialist training & maintenance

• images are black & white