Cell Theory
 The idea of cell started with
Robert Hooke.
 He first observed cork cells
and named the
compartments he saw
“cells”, named after the
rooms that monks lived in.
 Leeuwenhoek was one of the
first to look at living cells.
 He called the living things
he saw “animalcules”.
Cell Theory
 The cell theory grew out of the work of many scientists
and improvements in the microscope.
 Many scientists contributed to the cell theory.
 More was learned about cells
as microscopes improved.
 The cell theory is a unifying
concept of biology.
Cell Theory
 The cell theory has three principles.
 All organisms are made of cells.
Cell Theory
 The cell theory has three principles.
 All organisms are made of cells.
 All existing cells are produced by other living cells.
Cell Theory
 The cell theory has three principles.
 All organisms are made of cells.
 All existing cells are produced by other living cells.
 The cell is the most basic unit of life.
Cell Theory
 Prokaryotic cells lack a nucleus and most internal
structures of eukaryotic cells.
 All cells share certain characteristics.
Cell Theory
 Prokaryotic cells lack a nucleus and most internal
structures of eukaryotic cells.
 All cells share certain characteristics.

Cells tend to be microscopic.
Bacterium
(colored SEM; magnification 8800x)
Cell Theory
 Prokaryotic cells lack a nucleus and most internal
structures of eukaryotic cells.
 All cells share certain characteristics.


Cells tend to be microscopic.
All cells are enclosed by a membrane.
cell membrane
Bacterium
(colored SEM; magnification 8800x)
Cell Theory
 Prokaryotic cells lack a
nucleus and most internal
structures of eukaryotic
cells.
cell membrane
 All cells share certain
characteristics.



Cells tend to be microscopic.
All cells are enclosed by a
membrane.
All cells are filled with
cytoplasm.
cytoplasm
Bacterium
(colored SEM; magnification 8800x)
Cell Theory
 There are two cell types: eukaryotic cells and
prokaryotic cells.
Cell Theory
 There are two cell types: eukaryotic cells and
prokaryotic cells.
 Eukaryotic cells have a
nucleus.
nucleus
cell membrane
Cell Theory
 There are two cell types: eukaryotic cells and
prokaryotic cells.
 Eukaryotic cells have a
nucleus.
 Eukaryotic cells
have membraneorganelles.
nucleus
bound
organelles
cell membrane
Cell Theory
 There are two cell types: eukaryotic cells and
prokaryotic cells.
 Prokaryotic cells do not
nucleus
have a nucleus.
organelles
cell membrane
Cell Theory
 There are two cell types: eukaryotic cells and
prokaryotic cells.
 Prokaryotic cells do not
nucleus
have a nucleus.
 Prokaryotic cells do not
have membrane-bound
organelles.
organelles
cell membrane
cytoplasm
Cell Theory
 Some prokaryotic and some eukaryotic cells have
flagella.
 Flagella allow the organism to move the organism
through it’s environment.
Cell Theory
 Some eukaryotic cells have cilia.
 Cilia allow the organism to move the organism through
it’s environment.
 Cilia also can be used to move things along the cell’s
surface.

For example, cilia on the cells of the human respiratory system
sweep mucus and other debris out of the lungs.