1. Looking at Cells
Section 3.1

2. Cells Under the Microscope
Measuring Cell Structures
Measurements taken by scientists are expressed in metric units.
The official name of the metric system is the International System of Measurements, abbreviated SI.

3. 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.

4. Cells Under the Microscope, continued
Electron microscopes have much higher magnifying and resolving powers than light microscopes.

5. Types of Microscopes
Light microscopes form an image when light passes through one or more lenses to produce an enlarged image of a specimen.

6. 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.

7. 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.

8. 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.