Transcript cells - Biology I

CELLS
The Smallest Units Defined as Life
Wall Walk
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Aristotle
Gregorio Redi
Robert Hooke
Anton van
Leeuwenhoek
Lazzaro Spallanzani
Louis Pasteur
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Jean-Baptiste de
Lamark
Matthias Schleiden
Theoror Schwann
Rudolph Virchow
What is the Cell
Theory?
Aristotle 384-322 B.C.
“On the Generation of Animals”
• Discussed fundamental questions of life:
• How does reproduction occur?
• How does development occur?
• How does heredity take place?
“ … within each germ springs from a definite
parent and gives rise to a predictable progeny.
And thus it is the germ that is the ruling
influence and fabricator of the offspring."
Spontaneous Generation
From pre-historic times to about
1850, most people believed that under
the right conditions, living things
could spontaneously appear from
non-living material.
Francesco Redi 1668
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Born 1626 in Italy
First to challenge the idea of
spontaneous generation
Did not accept the common
belief that flies magically
appeared from rotting meat
Hypothesis: If a jar containing
rotting meat is covered, then it
will produce no flies
Redi’s Conclusions
Flies lay eggs,
which grow into
maggots, which
metamorphose
into flies
 If flies can’t lay
eggs, then no new
flies can grow
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We Object!
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Many people rejected Redi’s claim that flies
do not spontaneously generate
Their reasoning:
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“sealing the jar closed prevented a magical essence
from entering the rotting meat and brining it to
life”
“Scientists seek only to challenge belief systems
and stir things up”
THE MICROSCOPE
This instrument
opened up new
doors in the field of
biology; Galileo
designed a
compound
microscope
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1665-Robert Hooke
viewed thin slices of cork tree
under a crude microscope and
observed tiny hollow boxes.
He called these boxes cells.
Image Credit Cork cells
© 2010 Paul Billiet ODWS
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1674- Anton van Leeuwenhoek
observed tiny living organisms in
drops of pond water.
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Made over 250 microscopes
Caused a sensation and scared people!
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Lazzaro
Spallanzani
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1729. Italian
Believed microbes that spoil
food come from the air and
can be killed by boiling
Hypothesis: If air is allowed
to reach food, then microbes
will get in and cause it to
spoil
Spallanzani’s Experiment
Flask 1: boiled broth,
open
Flask 2: boiled broth,
sealed shut
Results
Flask 1 spoiled
Flask 2 did not spoil
Louis Pasteur 1862
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Anti-spontaneous generation experiments:
Improved on Spallanzani’s work
Pasteur definitively demonstrated that microorganisms are present in
air but not created by air. This was critical for refutation of the
concept of spontaneous generation and the for development of germ
theory of disease.
JEAN-BAPTISTE DE LAMARCK
1744-1829
The majority of this Frenchman's work dealt with
animal classification and evolution. He is credited
with taking steps towards the creation of the cell
theory with this saying:
"Every step which Nature takes when making her
direct creations consists in organizing into cellular
tissue the minute masses of viscous or mucous
substances that she finds at her disposal under
favorable circumstances
History of the Cell Theory
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1838- Matthias Schleiden concludes
that all plants are made up of cells.
History of the Cell Theory
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1839-Theodor Schwann
concludes that all animals are
made up of cells.
Created the term Cell
Theory
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History of the Cell Theory
1855-Rudolph Virchow completes
the cell theory by proposing all cells
come from existing cells.
 Demonstrated that the
Cell Theory applies to
diseased tissues as well
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The Cell Theory:
 All organisms are composed
of one or more cells
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Evidence?
The cell is the basic unit of
organization for the organism
 All cells come from preexisting cells
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Technology Connections
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Light Microscope 1600’s
Differential Centrifugation – 1930s
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Procedure to separate organelles from whole cells
Separate nucleus from cytoplasm
Transmission Electron Microscope
A beam of electrons instead of light is passed
through an ultra thin specimen; those that pass
through onto photographic plates
Scanning Electron Microscope
 Forms a 3D image of the specimen
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Two basic cell types:
Prokaryotic & Eukayotic
Prokaryotic cells
 Earliest cells
 Lack membrane bound organelles
 No nucleus
 No mitochondria
 Have membrane, cytoplasm, free DNA,
ribosomes
Prokayrotic cells:
Bacteria
Eukaryotic cells:
• May have evolved from
Prokaryotic cell
• Have a nucleus that holds the
DNA inside a membrane
• Have mitochondria
• Also have cell membrane &
cytoplasm
What are Organelles?
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Specific structures in the cytoplasm of the
cell
Perform specific functions for the cell
Organelles found only in plants include
 Cell walls
 Chloroplasts
Organelle found only in Animal
Cells
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Centrioles