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Chapter 3 Section 1: Microscopes

Chapter 3 Section 1: Microscopes. Cells Under the Microscope. Objectives:. Describe how scientists measure the length of objects. Relate magnification and resolution in the use of microscopes. Analyze how light microscopes function Compare light microscopes with electron microscopes.

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Chapter 3 Section 1: Microscopes

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  1. Chapter 3 Section 1: Microscopes

  2. Cells Under the Microscope Objectives: • Describehow scientists measure the length of objects. • Relatemagnification and resolution in the use of microscopes. • Analyzehow light microscopes function • Comparelight microscopes with electron microscopes. • Describethe scanning tunneling microscope.

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

  4. Cells Under the Microscope • Magnification is the quality of making an image appear larger than its actual size. • Resolution is a measure of the clarity of an image.

  5. Cells Under the Microscope • Both high magnification and good resolution are needed to view the details of extremely small objects clearly.

  6. Types of Microscopes

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

  8. Electron Microscopes • Electron Microscopes form an image of a specimen using a beam of electrons rather than light. • The electron beam and specimen must be in a vaccum so that the electron beam will not bounce off of gas molecules. • Live organisms cannot be viewed with an electron microscope.

  9. Transmission Electron Microscopes • 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.

  10. Transmission Electron Microscope • 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.

  11. Scanning Electron Microscopes • 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 a three-dimensional details of the surface of specimen.

  12. Scanning Tunneling Microscope • A needle-like probe measures difference 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.

  13. Scanning Tunneling Microscopes • The image shows a three-dimensional details of the surface of a specimen. • Live specimens and objects as small as atoms can be viewed.

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