Looking at CellsCells are VERY tiny!

centimeter= 1/100 of a meter (cm) =approximate width of the average fingernail

millimeter= 1/1000 of a meter (mm) =equivalent to the width of a pencil tip

micrometer= 1/1,000,000 of a meter (µm) = about the length of half of one E. Coli

nanometer= 1/1,000,000,000 of a meter (nm) about the size of a very large molecule

Cells are measured in micrometers, which is abbreviated as µm. A micrometer is equal to one millionth of a meter. Micrometers are also known as microns.

Some cells are only half a micron in diameter, which means you could fit two million cells along the width of a meter stick. They are naked to the human eye!

What came first? The cell or the microscope?

Anton van Leeuwenhoek’s microscope, established circa 1653

Cells, established billions of years ago

Anton van LeeuwenhoekA Dutch scientist born in 1632He did NOT invent the microscope, but he

did improve it. His new improved microscope was able to

see things that no man had ever seen before, i.e., bacteria, yeast, blood cells and many tiny animals swimming about in a drop of water. He called these “animalcules”.

Robert HookeRobert Hooke, an English scientist who was

the first scientist to give cells their name.When looking at a wine cork under a

microscope in 1665, he saw something similar to this:

Why do you suppose he named these structures “cells”?

1600’s

1700’s 1800

’s

Today

The origin of the microscope is a matter of debate. It is unclear as to who invented the very first microscope.

Classroom MicroscopeThe compound light microscope:The compound microscope has multiplelenses and needs a light source in order to magnify objects. This microscope is ideal for looking at a wide range of living or preserved specimens,though it can only magnify up to 1,000-2,000x larger.

Cells under a compound light microscope.

Electron MicroscopesAn electron microscope is any microscope that uses

a beam of electrons to form an image of a specimen. However, they are generally NOT used to view living specimens. The specimen is always dead and preserved.

There are three types of electron microscopes:1)Transmission electron microscope (TEM) – to be

discussed… 2)Scanning electron microscope (SEM)3)Reflection electron microscope

Transmission Electron Microscope (TEM)

Original electron microscopeInvented in the 1930s Can magnify an object 750,000x its original size.Capable of revealing a cell’sdetailed structure. Ideal for use on cells becauseTEM’s produce highly magnified3-dimensial images of the cell, as we will see in the virtual microscope!

http://school.discoveryeducation.com/lessonplans/interact/vemwindow.html

Scanning Tunneling MicroscopeInvented in the 1980’sCan magnify up to

2,000,000x an object’s original size. Safe for living specimens .Produces color images.Used to view atoms and

molecules- even cells are too big for the capacity of this amazing instrument!

Vocabulary 1. Resolution: a measure of the image clarity.

Example) unclear pictures= poor resolution

2. Magnification: making an image look larger than its actual size. This is done using lenses (like a magnifying glass or eyeglasses).

3. SI units: a system of measurement based on powers of 10. A compound microscope uses SI because its eyepiece lens is 10x.

Lenses of the Microscope and Total Magnification

Eyepiece (piece you look through) always has a 10x lens!

Objective Lenses (3-4 total)

4x

10x

40x

100x

Total magnification= eyepiece lens x objective lens! The microscope is currently set on the 10x objective lens.What is the total magnification?

Convex Lenses-It is very important to note that the eyepiece is

a CONVEX lens. -This is the same type of lens that is found in

our eyes.

The convex lens Inverts an image and makes itbackwards.

Image Quality

When you look at a specimen using a microscope, the quality of the image you see is assessed by the following:

•Brightness - How light or dark is the image?

•Focus - Is the image blurry or well-defined?

•Resolution - How close can two points in the image be before they are no longer seen as two separate points?

•Contrast - What is the difference in lighting between adjacent areas of the specimen?

Orlando Science Center March 2003

Brightness

Focus

Orlando Science Center March 2003

Resolution

Contrast

General Microscope Rules1) ALWAYS use two hands when handling the

microscope. One hand should hold the body tubeThe other hand should hold the base

General Microscope Rules2) When viewing your specimen, always start on the

LOWEST power first. This is always the shortest objective lens.

The lighted area that you see when you look through the microscope is called your FIELD of VISION.

By starting on low power you have the greatest field of vision and it is easier to find your object.

General Microscope Rules3) There are TWO focus knobs on the compound

microscope.

ALWAYS use the course adjustment first when focusing the specimen. Once the specimen is in view, NEVER touch the course adjustment, instead use the fine adjustment.

The course adjustment (bigger knob)

The fine adjustment

(smaller knob)

1

2

Course adjustment is used first (1) then the fine adjustment (2)

General Microscope Rules4) When done using the microscope, ALWAYS…

- Turn the microscope light off-Unplug the microscope-Put protective cover on microscope-Put microscope away if instructed to do so