Unit 4: Cells

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