MICROSCOPESAs tools for the biologist

How are microscopes useful?

• They are used to extend human vision by making enlarged images of objects.

• They are used to study organisms, cells, cell parts, and molecules.

Yeast cells

Light Microscopes

• Typically used to see small organisms and cells

• Compound light microscopes shine light through a specimen and uses two lenses to magnify the image

Four Main Parts of the Microscope• Eyepiece:Eyepiece: magnifies

the image (usually 10X)

• Objective Lenses: Objective Lenses: enlarge the image of the specimen from 2X to 100X

• Stage: Stage: platform that supports the slide

• Light Source: Light Source: provides the light for viewing the object

Magnification and Resolution• Magnification: Magnification: the

increase of an object’s apparent size

• Multiply the magnification of the ocular lens with the objective to get the total magnification

• Resolution: Resolution: is the power to show details clearly in an image

• Light microscopes are only useful up to 2000X

Onion cells at 100X magnification

Scanning Electron Microscopy• Passes a beam of electrons

over the specimen’s surface, providing a 3D view

• Spray the surface with a fine metal coating, the electron beam causes these to emit a shower of electrons

• Projects this image onto a fluorescent or photographic screen

• Magnifies up to 100,000X and you can look at living things

Pollen Grains

Open chamber of an SEM

Transmission Electron Microscope• Emits a beam of

electrons through a very thinly sliced specimen

• Magnetic lenses enlarge the image and focus it on a screen or photographic plate

• These can magnify objects up to 200,000 times

• Can only see dead things

Polio virus

TEM

Scanning Tunneling Electron Microscope• Looks at surfaces at the

atomic level

• Can see things at the nanometer scale (1,000,000,000X)

• Can be used from near 0 K to a few hundred degrees Celsius!!

Image of surface reconstruction on a clean Gold (Au(100)) surface, as visualized using scanning

tunneling microscopy. The individual atoms composing the material are visible. Surface reconstruction causes

the surface atoms to deviate from the bulk crystal structure, and arrange in columns several atoms wide

with regularly-spaced pits between them.