Download Cells: How their discovery led to the cell theory

Cells
and
The Cell Theory
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
Robert Hooke
in 1665 - First to
coin term – “Cell”
Looked at Cork
Looked really at a
dead plant cell
Only saw the cell
wall
Anton Van Leeuwenhoek
1600’s
Made lenses that
could magnify
more.
Observed many
living organisms
Looking at Protists
called them “Wee
Beasties” or
“animalcules”
(small animals)
Anton Van Leeuwenhoek
Leeuwenhoek’s
drawings of
“animalcules” set off a
flurry of amateur and
sometimes ridiculous
claims, such as:
- pondwater
animalcules causing
madness!
Anton Van Leeuwenhoek
-- looked at pond scum
-- looked at blood from different animals
-- looked at tartar from teeth
-- first person to see bacteria
--discovered yeast is a unicellular organism
(yes….yeast found is bread is a living thing!)
Birth of the cell theory…
1838 Matthias Schleiden –
concludes all plants made
up of cells
1839 – Theodore Schwann
concludes all animals are
composed of cells
Wrote 1st two parts of cell
theory.
Birth of the cell theory…
1858 Rudolph Virchow –
discovered that cells could
not develop from anything
except other cells
Wrote the third part of the
Cell Theory.
The Cell Theory
The cell theory has three parts:
All living things contain at least one cell
(Schwann)
The cell is the basic unit of life (Schwann)
Cells can only come from pre-existing cells.
(Virchow)
The Cell Theory
All living things contain at least one cell
Many scientists working
after Hooke and
Leeuwenhoek observed
different plants and animals
Each of them noted that no
matter what they observed,
if it was alive it had cells.
The Cell Theory
Cells are the smallest living units of matter
Scientists quickly realized that when
cells were dissected or broken open they
died
This meant that
whatever “life” is,
it is something that
happens inside cells
The Cell Theory
Cells can only come from pre-existing cells
does not answer the
question of where the first
cell came from or how it
came to be.
has not been disproved
yet - no scientist has ever
built a living cell from
nonliving organic
molecules
The cell theory is one of the
most important theories in
biology.
All living things contain at least one cell
Cells are the smallest living units of matter
Cells can only come from pre-existing cells
Cell Similarities
All cells have the following in common:
1. Cell Membranes
-surrounds the cell
-barrier between inside of cell and environment
-controls the passage of materials through the cell
2. Hereditary Material
-DNA
-controls activities of the cell
-contains the info needed to make new cells
Cell Similarities
All cells have the following in common:
3. Cytoplasm and Organelles
-organelles = structures that allow the cell to live,
grow, and reproduce.
-cytoplasm = the fluid inside a cell that surrounds
the structures.
4. Small Size
Benefits of Being Multicellular
Grow by producing more small cells, not
larger cells.
Can perform more functions than
unicellular.
Many kinds of cells
A single cell cannot do all the things
that many different things that cells
can do.
Two Types of Cells
1. Prokaryotic Cells
AKA = Bacteria
World’s smallest cells
NO NUCLEUS!
DNA is on long, circular molecule (rubber band)
Organelles do not have membranes
Have ribosomes (to make protein)
Most have a hard cell wall
Probably the first type of cells on Earth.
Oldest fossils ever found (3.5 billion yrs ago)
2. Eukaryotic
More complex than prokaryotic
10 times larger
Fossil evidence (2 billion yrs ago)
All living things (except bacteria) have eukaryotic
cells
Have a nucleus
All have cell membrane
Some have cell wall
Organelles have membranes
Have more DNA than prokaryotic
DNA stored in nucleus
DNA molecules are linear (not circular)
Prokaryotic vs. Eukaryotic
Prokaryotic
No nucleus
Organelles = no
membranes
DNA = circular
Bacteria
Eukaryotic
Nucleus
Organelles = have
membranes
DNA = linear (line)
All other cells
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.
People throughout the
Middle Ages believed
that mice could be
“created”
spontaneously by
putting grain in dark,
quiet place and leaving
it for a few weeks.
The discovery of
cells only
confused people
more- If cells are
alive, then where
do they come
from?
Can these almost invisible things
appear spontaneously from the
air?
Francesco Redi
Born 1626 in Italy
First to challenge the idea
of spontaneous generation
or biogenesis
Did not accept the
common belief that flies
magically appeared from
rotting meat
Redi’s Experiment
Independent variable =
cover
Dependent variable =
presence of flies
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
Fly eggs
Objections to Redi
Many people rejected Redi’s claim that flies
do not spontaneously generate
Their reasoning:
“sealing the jar closed prevented 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
1729. Italian
Believed microbes that spoil food
come from the air and can be
killed by boiling
Independent variable = air
Dependent variable = 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 shut
blocked the entrance of a
magical life force in the air
from getting to the broth.
Since few people had seen
these microbes, few people
believed him.
Louis Pasteur
1859. France
Supported that
spontaneous
generation is a myth
Invented
pasteurization
(sterilization by heat)
Pasteur’s Experiment
An improvement on Spallanzani’s work
Used special “swan-neck flasks” that allowed
air in but kept bacteria out
Independent variable = bacteria
Dependent variable = spoiling broth
Hypothesis; If boiled broth is kept free of
bacteria, then it will not spoil even if air can
reach it.
The curved neck allows air in but traps
bacteria-carrying dust and dirt particles
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.
Life from dead stuff= 0
Biogenesis = 3
Experimental method wins out over
superstition
the cell theory takes hold among
ordinary people
Pasteur is the father of
modern microbiology
supported the last part of the cell theory:
cells only come from pre-existing cells
identified yeasts as the microbes that
change grape juice into wine
showed that heat can be used to sterilize
foods and preserve them in sealed glass
containers, and later cans.
Finally...
in the late 1870’s,
doctors start to wash
their hands and
instruments before
operating...some even
start wearing gloves!
Joseph Lister’s wacky
idea that antiseptics kill
germs catches on...
The cell theory is one of the
most important theories in
biology.
All living things contain at least one cell
Cells are the smallest living units of matter
Cells can only come from pre-existing cells