# Looking at Cells.

## Presentation on theme: "Looking at Cells."— Presentation transcript:

Looking at Cells

Looking at Cells Cells 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 Leeuwenhoek A Dutch scientist born in 1632
He 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 Hooke Robert 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”?

1700’s 1800’s 1600’s Today The origin of the microscope is a matter of debate. It is unclear as to who invented the very first microscope.

Classroom Microscope The compound light microscope:
The compound microscope has multiple lenses 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 Microscopes An 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: Transmission electron microscope (TEM) – to be discussed… Scanning electron microscope (SEM) Reflection electron microscope

Transmission Electron Microscope (TEM)
Original electron microscope Invented in the 1930s Can magnify an object 750,000x its original size. Capable of revealing a cell’s detailed structure. Ideal for use on cells because TEM’s produce highly magnified 3-dimensial images of the cell, as we will see in the virtual microscope!

Scanning Tunneling Microscope
Invented in the 1980’s Can 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 Resolution: a measure of the image clarity. Example) unclear pictures= poor resolution Magnification: making an image look larger than its actual size. This is done using lenses (like a magnifying glass or eyeglasses). 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
4x 100x 40x 10x Objective Lenses (3-4 total) Total magnification= eyepiece lens x objective lens! The microscope is currently set on the 10x objective lens. What is the total magnification? Eyepiece (piece you look through) always has a 10x lens!

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 it backwards.

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?

Brightness Focus Orlando Science Center March 2003

Resolution Contrast Orlando Science Center March 2003

General Microscope Rules
ALWAYS use two hands when handling the microscope. One hand should hold the body tube The other hand should hold the base

General Microscope Rules
2) 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 Rules
3) 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 Rules
4) 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