Microscopes

The invention of the microscope in the 17th century led to the discovery of the cell.

Robert Hooke described cells using this light microscope.

Modern Microscopes

• Visible light is focused on the specimen with the condenser lens.

• Light passing through the

specimen is refracted with

an objective and an ocular

lens (magnify and invert the

image for the observer).

Two Important Properties of Microscopes:

• Magnification – how much larger an object is made to appear.

• Resolving power – minimum distance between two points that can still be distinguished as two separate points.

*limited by the wavelength of light.

*maximum resolution of a LM is 0.2μm.

*highest magnification is 1,000X.

Gallery of Cells

What can you infer about function from the structure of these cells?

Cell Theory

Electron Microscopes

• Instead of light, electron microscopes use electron beams which have much shorter wavelengths (resolving power of 0.2nm).

• Enhanced resolution and magnification led to the identification of subcellular organelles.

• There are two types of electron microscopes: transmission and scanning electron microscopes.

Transmission Electron Microscope

• Electromagnetic lenses.

• Electrons transmitted through the specimen are

focused onto a viewingscreen or film.

• Used to study internal cellular structure.

TEM Images

Scanning Electron Microscope• Electron beam scans the surface of the

specimen.

• Excites secondary electrons on sample.

• Collects secondary electrons and focuses onto a viewing screen.

• Great depth of field – 3D image.

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