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The Cell Theory
AP Biology
Some Random Cell Facts
 The average human being is composed
of around 100 Trillion individual cells!!!
 It would take as many as 50 cells to
cover the area of a dot on the letter “i”
WOW!!!
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Discovery of Cells
 1665- English Scientist, Robert Hooke,
discovered cells while looking at a thin slice of
cork.
 He described the cells as tiny boxes or a
honeycomb
 He thought that cells only existed in plants and
fungi
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Anton van Leuwenhoek
 1673- Used a handmade microscope to observe
pond scum & discovered single-celled organisms
 He called them “animalcules”
 He also observed blood cells from fish, birds,

frogs, dogs, and humans
Therefore, it was known that cells are found in
animals as well as plants
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150-200 Year Gap???
 Between the Hooke/Leuwenhoek


discoveries and the mid 19th century, very
little cell advancements were made.
This is probably due to the widely
accepted, traditional belief in
Spontaneous Generation.
Examples:
-Mice from dirty clothes/corn husks
-Maggots from rotting meat
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19th Century Advancement
 Much doubt existed around Spontaneous
Generation
 Conclusively disproved by Louis Pasteur
Pasteur: Ummm,
I don’t think so!!!
?
=
+
AP Biology
Development of Cell Theory
 1838- German Botanist, Matthias Schleiden,
concluded that all plant parts are made of
cells
 1839- German physiologist, Theodor
Schwann, who was a close friend of
Schleiden, stated that all animal tissues are
composed of cells.
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Development of Cell Theory
 1858- Rudolf Virchow, German physician,
after extensive study of cellular pathology,
concluded that cells must arise from
preexisting cells.
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The Cell Theory Complete
 The 3 Basic Components of the Cell
Theory were now complete:
 1. All organisms are composed of one or
more cells. (Schleiden & Schwann)(1838-39)
 2. The cell is the basic unit of life in all living
things. (Schleiden & Schwann)(1838-39)
 3. All cells are produced by the division of
preexisting cells. (Virchow)(1858)
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Modern Cell Theory
 Modern Cell Theory contains 4 statements, in
addition to the original Cell Theory:
 The cell contains hereditary information(DNA)



which is passed on from cell to cell during cell
division.
All cells are basically the same in chemical
composition and metabolic activities.
All basic chemical & physiological functions are
carried out inside the cells.(movement,
digestion,etc)
Cell activity depends on the activities of subcellular structures within the cell(organelles,
nucleus, plasma membrane)
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How Has The Cell Theory Been Used?
 The basic discovered truths about cells,
listed in the Cell Theory, are the basis for
things such as:

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Disease/Health/Medical Research and Cures(AIDS,
Cancer, Vaccines, Cloning, Stem Cell Research,
etc.)
Why Are Cells So Small?
Size Matters!
It’s all about:
Surface Area-to-Volume Ratio
Large
Cells
vs.
Small
Cells
Cell radius (r)
1 unit
10 units
Surface area (4╥r2) 12.57 units2
1257 units2
______
Volume (4/3╥r3)
4.189 units3
4189 units3
______
SA/V=
2.98
0.30
As a cell get larger, its volume increases at a faster rate than its surface area!
Eukaryote
Classification
 Old 5 Kingdom system
Prokaryote
 Monera, Protists, Plants,
Fungi, Animals
 New 3 Domain system

reflects a greater
understanding of evolution
& molecular evidence
 Prokaryote: Bacteria
 Prokaryote: Archaebacteria
 Eukaryotes




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Protists
Plants
Fungi
Animals
Archaebacteria
&
Bacteria
Kingdom
Bacteria
Kingdom
AP BiologyFungi
Kingdom
Archaebacteria
Kingdom
Protist
Kingdom
Plant
Kingdom
Animal
Prokaryotes
Domain Bacteria
Domain Archaebacteria
Domain
Bacteria
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Domain
Archaea
Domain
Eukarya
2007-2008
Common ancestor
Bacteria live EVERYWHERE!
 Bacteria live in all ecosystems
on plants & animals
 in plants & animals
 in the soil
 in depths of the oceans
Microbes always
 in extreme cold
find a way to
make a living!
 in extreme hot
 in extreme salt
 on the living
 on the dead

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Bacterial diversity
rods and spheres and spirals… Oh My!
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eukaryote cell
Prokaryote Structure
 Unicellular

prokaryote
cell
bacilli, cocci, spirilli
 Size

1/10 size of eukaryote cell
 1 micron (1um)
 Internal structure

no internal compartments
 no membrane-bound organelles
 only ribosomes

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circular chromosome, naked DNA
 not wrapped around proteins
Eukaryotes
Domain Eukarya
Domain
Bacteria
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Domain
Archaea
Domain
Eukarya
2007-2008
Common ancestor
eukaryote cell
Eukaryote Structure
 Unicellular or Multicellular

prokaryote
cell
Plant, animal, fungi, protist
 Size

10X larger than a prokaryote cell
 10-100 micron (1um)
 Internal structure


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Far more complex (compartmentalized)
 nucleus containing DNA
 other membrane-bound organelles
 ribosomes (no membrane)
Linear chromosome
 wrapped around proteins
Prokaryote vs. Eukaryote Chromosome
Prokaryote
Eukaryote
double helix
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mitochondria
Variations in Cell Interior
cyanobacterium
(photosythetic) bacterium
chloroplast
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aerobic bacterium
Prokaryote Cell Wall Structure
Gram-positive bacteria
peptide side
chains
cell wall
peptidoglycan
plasma membrane
That’s
important for
your doctor
to know!
protein
peptidoglycan = polysaccharides + amino acid chains
lipopolysaccharides = lipids + polysaccharides
Gram-negative bacteria
cell wall
outer membrane of
lipopolysaccharides
outer
membrane
peptidoglycan
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plasma
membrane
Prokaryotic metabolism
 How do bacteria acquire their energy &
nutrients?

photoautotrophs
 photosynthetic bacteria

chemoautotrophs
 oxidize inorganic compounds
 nitrogen, sulfur, hydrogen…

heterotrophs
 live on plant & animal matter
 decomposers & pathogens
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Genetic variation in bacteria
 Mutations

bacteria can reproduce every 20 minutes
 binary fission

error rate in copying DNA
 1 in every 200 bacteria has a mutation
 you have billions of E. coli in your gut!
 lots of mutation potential!
 Genetic recombination

bacteria swap genes
 plasmids
 small supplemental
circles of DNA
 conjugation
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conjugation
 direct transfer of DNA
Bacteria as pathogens
 Disease-causing microbes

plant diseases
 wilts, fruit rot, blights

animal diseases
 tooth decay, ulcers
 anthrax, botulism
 plague, leprosy, “flesh-eating” disease
 STDs: gonorrhea, chlamydia
 typhoid, cholera
 TB, pneumonia
 lyme disease
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Bacteria as beneficial (& necessary)
 Life on Earth is dependent on bacteria

decomposers
 recycling of nutrients from dead to living

nitrogen fixation
 only organisms that can fix N from atmosphere
 needed for synthesis of proteins & nucleic acids
 plant root nodules

help in digestion (E. coli)
 digest cellulose for herbivores
 cellulase enzyme
 produce vitamins K & B12 for humans

produce foods & medicines
 from yogurt to insulin
AP Biology
How big are cells?
 Microscopic


(mostly)
Measured in
microns µm
(micrometers)
.
 A µm is one
millionth of a
meter =
 10-9 m = one
thousandth
of
AP
Biology
How big are cells?
Smallest free-living cell =
Mycoplasma genitalium
Size = 0.2 to 0.3 µm
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How big are cells?
 Bacteria e.g. Eschericia coli (aka
E.coli)
 Size=1 µm by 3 µm
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How big are cells?
 Human red blood cell = 8 µm in
diameter
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How big are cells?
 Largest cell on
the human
body =
ovum
 Size=
 1000 µm in
diameter
(1 mm)
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How big are cells?
 Smallest cell in the human body =
sperm cell.
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How big are cells?
 Largest cell with a
metabolism =
Chaos chaos
Size=1-5 mm in
length.
common name =
Giant Amoeba
osAP
diffluens,
is an amoeba closely related to the giant amoebae
Biology
How big are cells?
 Largest cell = yolk of an ostrich egg
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Ostrich, egg, humans
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Ostrich emerged from egg
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How can we study cells?
Problem:
They are microscopic!
Solution:
Use a microscope!
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Types of Microscopes
1. Compound light
microscope


Light passes
through lenses to
magnify image up
to 1000X
Can observe
living cells
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Types of Microscopes
2. Electron
microscope


Uses a beam of
electrons to
magnify image
> 1000X
Kills cells being
observed
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