Cell Theory Notes
In the 1800’s, many people thought that life could come from nonliving things!
Examples:
 Earthworms fell from the sky after it rained.
 Jan Baptist van Helmont said you could get mice from
grain put in a corner with rags over it.
This theory was called spontaneous generation (living things
could come from nonliving matter.)
In 1668, a doctor, Francesco Redi, disproved a commonly
held belief that flies came from rotting meat.
It took 200 years and many more experiments (Spallanzani, Pasteur, etc.) to disprove these previous
theories and prove that….. life comes from only life!
This theory is called biogenesis (living things come from only other living things).
In 1665, Robert Hooke was the first to use the term “cell” to describe the tiny spaces he saw in cork.
In the 1670-1680’s, Anton von Leeuwenhoek did not invent the microscope but made the first “good”
microscopes because of his excellent lens grinding abilities. He was the first to see tiny creatures in
pond water. He called these creatures “wee beasties”.
Leeuwenhoek is known as the father of microbiology!
Putting it all together--- In 1838, Matthias Schleiden concluded that all plants were made up of cells.
 In 1839, Theodor Schwann concluded that all animals were made up of cells.
 In 1854, Rudolph Virchow hypothesized that cells divide to form new cells.
The Cell Theory:
1. All organisms are made up of one or more cells.
2. Cells are the basic unit of structure and function in all organisms.
3. All cells come from cells that already exist.
*The cell theory in one of the major theories in science. It is the result of the discoveries of MANY
scientists not just a few. It serves as the basis for today’s scientists who are studying parts of the
cells, how cells are organized, and how cells and organisms reproduce and change through time.
In class we used a compound microscope, but there are different types of microscopes:
1. Simple microscopes- similar to a magnifying glass, It has only one lens.
2. Compound Light Microscope- a microscope with 2 or more lenses and was
invented by Zacharias Janssen in 1590. It uses light to pass through the object and
then the lenses. Today, light microscopes can magnify up to about 500x.
3. Electron Microscope- uses beams of electrons bent by magnetic fields to enlarge
objects. They can magnify up to about 300,000x.
There are two main kinds of electron microscopes:
1. Transmission electron microscope (TEM)- used to see great detail inside cells,
ect.
2. Scanning electron microscope (SEM)- used to see a three-dimensional picture of whole
objects.
Levels of Organization
The Cell Theory states that all organisms are made of cells. There is an order that these cells make
up an organism and this order is shown below:
Cells (Animal)

Tissue

Organ 
Cells make up
Tissues make up
Organs make up
Organ System

Organism
Organ Systems make up
An Organism!
Cells (plant)

Tissue (layer of a leaf) 
Organ (Leaf)
 Organ System /Organism