The Microscope

Microscope History Microscopes are instruments which produce a magnified image to help us to examine small objects and their fine details which our eye cannot see. Microscopes range from simple devices such as a magnifying glass up to high end compound or electron microscopes .

Early Microscopes Simple Microscope Compound Microscope

Microscopes used today Compound Microscope

There are similarities in all microscopes: Magnify a small object Separate fine details in order to achieve a high resolution

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Types of Microscopes Simple Dissecting Compound Scanning Electron Microscope (SEM) Transmission Electron Microscope (TEM).

Using a Microscope to Explore the Cell Resolution or Resolving power The ability to distinguish between two objects that are close together High resolution Low resolution 8

1. Simple Microscope Similar to a magnifying glass and has only one lens A lens enlarges an image and bends the light toward your eye.

2. Compound light microscope Light source: Lamp Resolution: limited to about 0.2 µm (micrometers) Magnification: 2000X 2 D image produced Image seen: In eyepiece Specimen Preparation: Stain cells on a slide Type of specimens can be used: Both 10

Total Magnification To get the total magnification: Eyepiece Lens X Objective Lens = Total Magnification

Low Power = 4 x Medium Power = 10 x High Power = 40 x

3. Electron Microscope Used to see objects that are smaller than 2µm There are 2 types of electron microscopes: A. Transmission Electron B. Scanning Electron

A. Transmission Electron Microscope (TEM) How it works: Light Source: Electrons pass through Resolution: 0.0002 µm Magnification: 500,000x Type of image: 2 D Where image is seen: On a screen/ monitor Specimen preparation: Very complex Types that can be used: Dead

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B. Scanning Electron Microscope (SEM) How it works: it passes a narrow beam of electrons over the surface of a specimen. The specimens must be coated with a very thin film of metal, usually gold.  As electrons bounce off the specimen a television screen picks up the image. It produces a 3-D image.

Light Source: Electrons pass over surface of specimen How it works: Light Source: Electrons pass over surface of specimen Resolution: 0.005 µm Magnification: 300,000x Type of image: 3 D Where image is seen: On a screen/ monitor Specimen preparation: Sprayed with gold Types that can be used: Dead or alive

Mitochondria in human liver cell 21

TEM SEM Magnification: 500,000x Resolution: 0.0002 µm Magnification: 300,000x Resolution: 0.005 µm *** SEM have lower resolutions than TEM, but they have the advantage of providing 3-D images Some specially designed SEM’s allow you to observe living specimens

1. Compound Light Microscope (pg.20) Consists of 2 lens Light Source: light (passes through specimen) Resolution: 200nm or 0.2µm Magnification: 2000x Image produced: 2D Where image is seen: Eyepiece Specimen Prep: Slicing/staining Type of Specimen: Dead or alive

2. Transmission Electron Microscope (TEM) Light Source: electrons (passed through specimen) Resolution: 0.2nm or 0.0002 µm Magnification: 500,000x Image produced: 2D Where image is seen: Projected on screen/monitor = picture! (internal study) Specimen Prep: very complex – cross sections Type of Specimen: Dead

3. Scanning Electron Microscope (SEM) Light Source: electrons (passed through specimen) Resolution: 5 nm or 0.005 µm Magnification: 300,000x Image produced: 3D Where image is seen: Projected on tv screen (study surface of specimen) Specimen Prep: Sprayed with gold coating Type of Specimen: Dead or alive