The Microscope

Basic information Microscopes are devices that produce magnified images of structures that are too small to see with the unaided eye Two types of microscopes: Light microscopes Electron microscopes

Light microscopes The first type of microscope Works by passing visible light through a specimen Can magnify objects only about 1000 times (1000X)

Compound light microscope Used at NOHS – uses two lenses to form the image

Compound Light Microscope

Magnification Eyepiece: 10X Three objectives: Total magnification Low: 4X Medium: 10X High: 40X Total magnification Eyepiece x objective lens

Light microscope Magnification: number of times larger the image appears than the object actually is Resolving power: the clarity of the object An optical device is limited by its resolving power Light microscopes cannot show the details of the cell’s internal structure.

Electron Microscope Uses a beam of electrons instead of light Developed in 1950s to view smaller objects Can only be used to view dead and preserved cells No color Expensive Has a higher resolving power than the light microscope Can magnify about 100,000 times

Scanning electron microscope Used to study the detailed architecture of cell surfaces SEM composes images on a TV screen from the electrons that bounce off the surfaces of the object. SEM images are usually about 10,000 to 20,000 times larger than life size. Useful for showing organisms and cellular surfaces under high magnification Can produce three-dimensional images

Scanning electron microscope

Transmission electron microscope Used to study the details of internal cell structure Composes images on camera film Images are usually 100,000-200,000 times larger than life size Useful for showing the internal structure of cells

Transmission electron microscope

Main problem Electron microscopes cannot be used to study living specimens because the specimen must be held in a vacuum chamber—all air and liquid must be removed. We still use the light microscope for studying living cells.

Parts of the Microscope Eyepiece: contains the magnifying lens Arm supports the body tube Fine adjustment knob sharpens the image Coarse adjustment knob brings the image into a rough focus Base supports the microscope Diaphragm regulates the amount of light passing up toward the eyepiece Low power objective is the shortest lens (4X) High power objective is the longest (40X) Nosepiece holds the objectives

Parts of the microscope

Scientists to Remember Anton van Leeuwenhoek: first to use a simple microscope to study nature Robert Hooke: used a light microscope to look at cork; called small chambers in cork “cells”

Using the microscope Always carry the microscope with one hand on the arm and one hand on the base Always begin your study with the low power objective in place Only use the coarse adjustment knob with the low power objective Only clean the lens of the microscope with clean lens tissue. When you finish using the microscope you should always remove the slide and store the microscope with the low power objective in place