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

Total Magnification = Objective x eyepiece magnification magnification

10x

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)

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

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

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 visible light

Light shines through an object and lenses magnify the image

Up to 1000 x

Specimens must be thin and transparent.

Can be living or dead.

Beams of electrons emitted 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

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