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 To render the object against the adjacent background to achieve an acceptable contrast

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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

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

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

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

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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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

How to use a compound microscope Use the scanning objective (smallest) and bring it into focus using the LARGE KNOB (coarse adjustment) Switch to low power (medium) and refocus using the LARGE KNOB.   You can re–center the image if necessary. Switch to high power (biggest) and ONLY focus with the small knob (fine adjustment) **DO NOT USE THE COARSE ADJUSTMENT ON HIGH POWER – YOU WILL BREAK YOUR SLIDE**

Questions 1. Explain how to determine (a) The highest magnification of a compound light microscope (b) The diameter of the field of view. 2. How much larger does a grain of sand appear to be under a microscope. if the magnification of the objective lens is 4x and the magnification of the eyepiece lens is 15x? 3 . Read pages 20-21 in textbook

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