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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. - PowerPoint PPT Presentation
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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
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
http://glencoe.mcgraw-hill.com/sites/0078695104/
http://www.denniskunkel.com/
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