1. Cell Theory and the Microscope
Looking at Cells
Cell Theory and the Microscope

2. The Cell Theory
The Cell Theory arose after hundreds of years of observation, and many scientists. A few key scientists involved in the cell theory are Hooke, Schleiden, Schwann and Virchow.
Robert Hooke- The first scientist to describe what he saw as “cells” when viewing samples of cork under the microscope in 1665.

3. The Cell Theory
Nearly 200 years later, Matthias Schleiden viewed living plant specimens under the microscope and discovered they were made up of cells.
Around the same time as Schleiden, Theodor Schwann viewed nonliving animal parts under a microscope and realized that they, too were made up of cells.

4. The Cell Theory
Finally, Rudolf Virchow witnessed cell division under the microscope and learned that all cells arise from preexisting cells.
The findings of these scientists, among others, lead to the cell theory, which states:
All living things are made of cells.
Cells are the basic unit of structure and function of life.
Cells come from preexisting cells.

5. What came first? The cell or the microscope?
Anton van Leeuwenhoek’s microscope, established circa 1653
Cells, established billions of years ago

6. 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.

7. 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”.

8. Looking at Cells
Measurement Review!
centimeter= 1/100 of a meter (cm) =approximate width of a 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

9. Looking at Cells
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 length of a meter stick. They are naked to the human eye!

10. 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.

11. 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.

12. Lenses of the Microscope and Total Magnification4x
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!

13. 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.

14. 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 – A measure of the definition of the image. Is the image blurry or well-defined?
Resolution - the smallest distance between two objects at which the objects still appear to be separate from one another; measures the clarity of the image (allows details to be observed).
Contrast– The difference in lighting between adjacent areas of the specimen.

15. Orlando Science Center March 2003
Brightness
Focus
Orlando Science Center March 2003
Orlando Science Center

16. Orlando Science Center March 2003
Resolution
Contrast
Orlando Science Center March 2003
Orlando Science Center

17. Parts of the Light Microscope
eyepiece
body tube
nose piece
arm
objective lenses
stage
stage clips
course adjustment
diaphragm
fine adjustment
light source
base

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

19. 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.

20. General Microscope Rules
There are TWO focus knobs on the compound microscope.
The course adjustment (bigger knob)
The fine adjustment
(smaller knob)
3) Always use the course adjustment
first when focusing the specimen.
Once the specimen is in view, then move on to the the fine adjustment.

21. 1 2
Course adjustment is used first (1) then the fine adjustment (2)

22. 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 where you found it.