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Cell Theory
2012-13
History
• Cells were unknown
until the invention of
microscopes in the
1650’s
• two scientists working
independently built the
first microscopes
– Anton von
Leeuwenhoek in
Holland
– Robert Hooke in
England
Anton von Leeuwenhoek
• Studied pondwater, sour milk,
and semen
• named moving organisms
“animalcules”
Anton von Leeuwenhoek
People
thought
human
sperm cells
contained
tiny human
beings
called a
homunculus
Robert Hooke
• Studied cork - a
kind of tree bark
• named the
structures he
saw “cells”
because they
reminded him of
the small rooms
monks slept in.
The Cell Theory
• The cell theory has three parts:
–All living things contain at least one
cell
–Cells are the smallest living units of
matter
–Cells can only come from preexisting cells
All living things contain at least
one cell
–Many scientists have observed
different plants and animals
–Each of them noted that no
matter what they observed, if it
was alive it had cells.
Cells are the smallest living
units of matter
–scientists realized that when cells
were dissected or broken open they
died
–This meant that whatever “life” is, it
is something that happens inside
cells
Cells can only come from preexisting cells
–Except the first cell
–has not been disproved
yet- no scientist has ever
built a living cell from
nonliving molecules
Spontaneous Generation
• Until 1850, most people
believed that living things
could spontaneously appear
from non-living material
Spontaneous generation
• People believed that mice could be
“created” spontaneously by putting
grain in dark, quiet place and leaving
it for a few weeks.
• Scientists sought to disprove it
Francesco Redi
• First to challenge
spontaneous
generation
• Did not accept
that flies
appeared from
rotting meat
Redi’s Experiment
– IV= cover
– DV= presence of
flies
– Hypothesis: If a
jar containing
rotting meat is
covered, then it
will produce no
flies
Redi’s Conclusions
–Flies lay
eggs, grow
into maggots,
grow into flies
–If flies can’t
lay eggs, then
no new flies
Objections to Redi
–“sealing the jar closed kept a
magical essence from entering
the rotting meat and bringing it
to life”
–“Scientists seek only to
challenge belief systems and
stir things up”
Lazzaro Spallanzani
• microbes that spoil food come from the air
and can be killed by boiling
• IV= air, DV= food spoilage
• 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
Objections to Spallanzani
• Sealing the flask blocked the
magical life force in the air from
getting to the broth.
Louis Pasteur
• 1822. France
• Supported that
spontaneous
generation is a
myth
• Invented
pasteurization
(sterilization by
heat)
Pasteur’s Experiment
• Used special
“swan-neck
flasks” that
allowed air in
but kept
bacteria out
Pasteur’s Experiment
• IV= bacteria,
DV= spoiling broth
• Hypothesis; If
boiled broth is kept
free of bacteria,
then it will not spoil
even if air can
reach it.
Spontaneous generation is
dead!
• Redi didn’t believe in it, and did
an experiment using flies
• Spallanzani didn’t believe in it,
and experimented with broth
• Pasteur disproved it conclusively
with his open-air yet spoilage free
flasks.
Pasteur is the father of modern
microbiology
• supported the last part of
the cell theory: cells only
come from pre-existing cells
• showed that heat can be
used to sterilize foods and
preserve them
As a result…
• in the late 1870’s, doctors start to
wash their hands and instruments
before operating...some even
start wearing gloves
Organelles are
membrane-bound cell
parts
•Mini “organs” that have
unique functions
•Located in cytoplasm
(everything inside the
cell membrane)
Cells have evolved two
different architectures:
• Prokaryote
• Eukaryote
Prokaryote cells are smaller and
simpler
• Commonly known as bacteria
• Single-celled (unicellular) or
• Filamentous (strings of single
cells)
Prokaryote cells
• These are
prokaryote
• E. coli
bacteria on
the head of a
steel pin.
Prokaryote Cells
• cytoplasm:
inner liquid
filling
• DNA in one big
loop
Prokaryote Cells
• ribosomes:
for building
proteins
Endosymbiont theory:
•a prokaryote
ancestor “eats” a
smaller
prokaryote
•They join forces
and become
more complex
•
Eukaryotes
• Bigger and more complex
• Have organelles
• Have chromosomes
• can be multicellular
• include animal, plant, fungal,
and protist cells
Cell Structures
•Cell membrane
–delicate
phospholipid and
protein skin around
cytoplasm
–found in all cells
•Nucleus
–a membranebound sac evolved
to store the cell’s
chromosomesDNA
–has pores: holes
•Nucleolus
–inside
nucleus
–location of
ribosome
factory
–made of RNA
•mitochondrion
– makes the cell’s
energy
–the more energy
the cell needs, the
more
mitochondria it
has
•Ribosomes
–build proteins
from amino acids
in cytoplasm
–may be freefloating, or
–may be attached
to ER
–made of RNA
•Endoplasmic
reticulum
–may be smooth:
builds lipids and
carbohydrates
–may be rough:
stores proteins
made by attached
ribosomes
•Golgi
Complex
–takes in sacs
of raw material
from ER
–sends out sacs
containing
finished cell
products
•Lysosomes
–sacs filled with
digestive
enzymes
–digest worn
out cell parts
–digest food
absorbed by cell
•Centrioles
–pair of bundled
tubes
(microtubules)
–organize cell
division
Cytoskeleton
•found
throughout
cytoplasm
•gives shape to
cell & moves
organelles
around.
Structures found in plant cells
•Cell wall
–very strong
–made of
cellulose
–protects cell
from rupturing
•Vacuole
–huge waterfilled sac
–keeps cell
pressurized
–stores starch
•Chloroplasts
–filled with
chlorophyll
–turn solar
energy into
food energy
Eukaryote cells can be
multicellular
•The whole cell can be specialized
for one job
•cells can work together as tissues
•Tissues can work together as
organs
Label the cells