Cells!
Section through human skin
Smear of skin cells
Nerve cell
Bone cells
White blood cell attacking bacteria
Muscle Cells
Heart cells
http://learn.genetics.utah.edu/conte
nt/begin/cells/scale/
THE CELL THEORY
The Cell Theory
 Theory:
An idea or explanation that is accepted to be true
based on numerous scientific investigations
which support it, while none can refute it.
A theory can be adjusted according to new
investigations, but will never be completely
disproved.
The Cell Theory
 The invention of the microscope was
the key to discovering cells!
Anton von
Leeuwenhöek
 1632-1723
 Inventor of the microscope.
 Inspired by lenses used to examine
drapery cloth.
 The first person to observe and
describe microscopic organisms and
cells.
ROBERT HOOKE
 This English naturalist (1635 - 1703)
 Coined the term "cell" after viewing slices of cork
through a microscope.
 The term came from the Latin word cella which means
"storeroom" or "small container".
Rudolf Virchow
 German pathologist Rudolf Virchow
(1821 - 1902).
 “Every cell comes from a cell".
Other Scientists
 1824-Henry Dutrochet: all living things are made up
of cells
1831- Robert Brown: discovered cell nucleus
(not function)
1838- Matthias Schleiden: all plants are made of
cells
1839- Theodor Schwann: all animals are made of
cells
The Cell Theory
consists of THREE Principles:
1. All living things are composed of
one or more cells.

Cells are the basic units of structure
and function in an organism.
2. All cells carry on life activities.
3. Cells come only from
reproduction of pre-existing
cells.
Exception #1
 Viruses: can reproduce inside a living host cell but
are not considered living cells
Viruses
 Officially, are not alive.
 They cannot do any of the life processes without
the help of another cell.
Viruses
 Are not made of cells.
Virus
vs Bacteria
 Inject DNA into your
cells and kill them.
• Reproduce in your
body, feeding off of
you.
 Can only be prevented
BEFORE infection
with a vaccine.
• Can be killed with
antibiotics AFTER
infection.
Exception #2
 First cells?- Could not have come from other cells so
where did they come from?
Exception #3
 Mitochondria and Chloroplasts have genetic material
and can duplicate themselves
Review
 What are the 3 principles of cell theory?
Cell Theory
All organisms are made of one
or more cells
Cell Theory
 All cells carry on all life functions
Cell Theory
All cells arise from pre-existing
cells