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Cell Theory
(Ch. 7 Section 1)
Historical Background - Hooke
• Term “cell” first used by
Robert Hooke (1665,
England)
• He looked at cork plant
samples through an early
compound microscope
• The empty cork chambers he
called cells.
• Also made great discoveries
in physics, chemistry,
astronomy and architecture
Historical Background Leeuwenhoek
• Dutch, mid-1600’s
• Father of Microbiology
• Perfected early microscopes
and their use
• Discovered single-celled
organisms
• First to make many
observations at the cellular
level: bacteria, muscle fibers,
blood flow, etc…
Historical Background –
Germans
• 1838 – Schleiden: all plants are made of
cells
• 1839 – Schwann: all animals are made of
cells
• 1855 – Virchow: new cells can only
emerge from two previous cells dividing
• All of these discoveries lead to the Cell
Theory
Cell Theory
Cell Theory basically states 3 things:
1) All living things are composed of cells
(some unicellular, some multi-cellular)
2) Cells are the basic unit of structure and
function in living things
(Different cell types look and function
differently)
3) New cells are produced from existing
cells
(different types of cell division)
New discoveries…
• Cellular structure and
function is very complex
• Cells seem to have their
own machinery
• Organelles work together
to make the cell a small
factory – more complex
and efficient than any
human factory
• Discoveries made possible
by better microscopes,
biochemistry, DNA
research
Better Scopes
• Transmission Electron Microscopes (TEM’s):
electrons pass through thins slices of
specimens to create the image
• TEM’s show cell structure and protein
molecule structure
• Scanning Electron Microscopes (SEM’s):
electrons bounce off specimen to create a 3D image
Electron microscopes can only work in a
vacuum so only non-living, preserved
specimens can be used
Pollen under SEM
Better Scopes
• Scanning Probe
Microscopes developed
in 1990’s use a probe
instead of an electron
beam
• Can even show images
at atomic level
• Vacuum not necessary
• Used to show protein
structure, DNA, other
cellular structures
Arrangement
of atoms on
silicon
surface
Prokaryotic vs. Eukaryotic
• All cells are bound by a cell membrane and at
some point carry DNA
• Prokaryotic cells have no nucleus to hold the
DNA
• Eukaryotic cells have a nucleus as well as
other internal membranes
• Eukaryotic cells are more complex
• Eukaryotic cells are generally larger
• Bacteria – Prokaryotic,
• Most others – Eukaryotic