Looking at CellsSection 3.1

Cells Under the Microscope

Measuring Cell StructuresMeasurements taken by scientists are expressed

in metric units. The official name of the metric system is the

International System of Measurements, abbreviated SI.

Cells Under the Microscope, continued

Magnification is the quality of making an image appear larger than its actual size.

Resolution is a measure of the clarity of an image.

Both high magnification and good resolution are needed to view the details of small objects clearly.

Cells Under the Microscope, continuedElectron microscopes have much higher magnifying and

resolving powers than light microscopes.

Types of Microscopes Light microscopes

form an image when light passes through one or more lenses to produce an enlarged image of a specimen.

Types of Microscopes, continued

Transmission Electron Microscope

An electron beam is directed at a very thin slice of a specimen stained with metal ions. Some structures become more heavily stained than others.

The heavily stained parts absorb electrons, those that are lightly stained allow electrons to pass through.

The electrons that pass through strike a fluorescent screen, forming an image.

Types of Microscopes, continued

Scanning Electron Microscope

An electron beam is focused on a specimen coated with a very thin layer of metal.

The electrons that bounce off the specimen form an image on a fluorescent screen.

The image shows three-dimensional details of the surface of a specimen.

Types of Microscopes, continued

Scanning Tunneling Microscope

A needle-like probe measures differences in voltage caused by electrons that leak, or tunnel, from the surface of the object being viewed.

A computer tracks the movement of the probe across the surface of the object.

The image shows three-dimensional details of the surface of a specimen.

Live specimens and objects as small as atoms can be viewed.