Unit 4: Cells Microscopes and the Discovery of Cells

Objectives: At the end of this lesson, students will be able to:  Compare and contrast light microscopes and electron microscopes.  Identify the parts of the compound light microscope and explain their function.  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 –

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

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)

Transmission Electron Miscroscopy Sperm flagellum (cross section)

Transmission Electron Microscopy Bacteriophages (viruses that infect bacteria)

Human atrial (heart) muscle Transmission Electron Miscroscopy

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  hill.com/sites/ / hill.com/sites/ / 

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

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? Light Light shines through an object and lenses magnify the image 1000 x Specimens must be thin and transparent. Can be living or dead. Electrons Fixed specimens are placed in a vacuum. Electrons are transmitted through or scan the outside of the object. Fixed specimens must be dead, dry, and stained with heavy metals. Usually 35,000 x but can be 1 million x Comparing Microscopes

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