Unit 4: Cells Microscopes

Objectives: At the end of this lesson, students will be able to: Identify the parts of the compound light microscope and explain their function. Calculate the total magnification of a compound light microscope. Compare and contrast light microscopes and electron microscopes. Demonstrate how to prepare a wet mount and properly focus a compound light microscope.

The Compound Light Microscope Uses visible light to produce an image. Specimens must be thin. Why? Specimens can be alive or dead. Can magnify objects up to 1000x –

Compound Light Microscopes Compound = “multiple” Light = type of radiation that conveys the image

Resolution the ability of the microscope to make individual components visible visible light scatters limits magnification of light microscopes to 1000x

The Compound Light Microscope Four systems Focusing Lens Light Stage “Focused Lenses Light the Stage”

Calculating Magnification 10x Total Magnification = Objective x eyepiece magnification magnification

Transmission Electron Microscopes Uses magnets to aim a beam of electrons at thin specimens in a vacuum. Produces a black & white image based on electron absorption. Magnify up to 500,000x (practically about 35,000x) Specimen must be dead and stained with heavy metals. Transmission Electron Microscope (TEM)

How an Electron Microscope Works

Transmission Electron Miscroscopy Sperm flagellum (cross section)

Transmission Electron Microscopy Bacteriophages (viruses that infect bacteria)

Transmission Electron Miscroscopy Human atrial (heart) muscle

Scanning Electron Microscope Can magnify objects up to 1 million times (usually 35,000x) Specimens can be in gross form. Image is made of the surface of the object. Electrons are bounced off an object and collected on a photographic plate. Specimens must also be dry, dead, and stained with heavy metals. Scanning Electron Microscope (SEM)

Scanning Electron Microscopy Stainless Steel Screen

Scanning Electron Miscroscopy Table Salt

Scanning Electron Miscroscopy Insect on the leg of a daddy long-leg spider

Scanning Electron Miscroscopy Eye of an Ant

Scanning Electron Miscroscopy Spider

Other images Human Histology - mostly light microscope images Dennis Kunkel Microscopy Inc.

Compare & Contrast SEM & TEM From these images include in your notes some similarities & differences between SEM images and TEM images

Comparing Microscopes Light microscopes Electron microscopes What is used to make an image? How does it magnify objects? How well can it magnify? What can it magnify? What can it record? Beams of electrons emitted in a vacuum Beams of visible light Light shines through an object and lenses magnify the image Electrons are transmitted through or scan the outside of the object. Usually 35,000 x but can be 1 million x Up to 1000 x Specimens must be thin and transparent. Can be living or dead. Fixed specimens must be dead, dry, and stained with heavy metals. Full color images. Can be captured using digital camera or computer Computer captures digital black & white images that can be colorized.

Homework – due January 4, 2012 Read Using a Compound Light Microscope Laboratory. Answer the Pre-Lab questions on a separate sheet of paper to be handed in at the beginning of laboratory tomorrow. Goggles and apron are not required tomorrow.

Scanning Tunneling Microscope Uses the charged tip of a probe to get very close to the specimen. Electrons “tunnel” between the probe and the specimen. Creates three dimensional computer images of live objects and even atoms. STM of DNA molecule