Download Cell Theory: Discovery of the Cells and its Theory

Cell Theory: Discovery of
the Cells and its Theory
Chapter 7.1
History
• Cells were not discovered until the
development of the microscope in the
1650s
• Two scientists working separately of each
other built the first microscopes:
• Anton von Leeuwenhoek in Holland
• Robert Hooke in England
Leeuwenhoek
• Studied pond water, sour milk, and semen
• The first person to see cells under the microscope
• Names moving organisms “animacules” (there was no
other name for cells at this time!)
• Scared people and caused a sensation
Leuuwenhoek’s Drawings of “animacules”
• These drawings led to
ridiculous claims
• “Pond water causes
madness!!”
And….
• They thought human
sperm cells contained
tiny human beings and
reproduction worked like
planting a seed. The
human grew out of the
cell!
• We look back and think
this is “crazy” but at the
time, people took these
ideas very seriously!
Hooke
• Studied Cork- kind of tree bark (plant cells)
• The first person to coin the term “Cell”
• Named them cells because they reminded him of the
small rooms (cells) that monks slept in
The Cell Theory
• Many men contributed to the discovery of the cell theory
and what we know about cells now
• Theodore Schwann (all animals made of cells)
• Mathias Scheiden (all plants made of cells)
• The cell theory states that cells:
• are the basic unit of life
• can only come from prior cells
• all living things are made of at least one cell
How did they determine this?
• When cells were dissected or broken open, they died
• This meant that whatever “life” is, it is something that
happens inside cells
• Observations of many living things were made and if it
was alive, it had cells
Cells come from pre-existing cells
• Does not answer the question where the first cell came
from or how it came to be
• The idea is now disproved that life can come from nonlife
• No scientist has ever built a living cell from non-living
organic molecules
Spontaneous Generation
• Idea that was believed to be true up until about 1850
• Spontaneous generation says that life could arise from
non-living things
• Life can be “spontaneously” created, also called
abiogenesis (life not from life)
• Today we believe in biogenesis (life from life)
Spontaneous Creation in mice idea
• People in the Middle Ages
believed that mice could
be spontaneously created
by putting grain in a dark,
quiet place and leaving it
for a few weeks. They
thought the bag of grain
would produce the mice!
Disproving Spontaneous Generation
• The following scientists attempted to disprove the idea of
spontaneous generation; they believed life came from
life:
• Francesco Redi
• Lazzaro Spallazani
• Louis Pasteur
Redi
• Italian scientist, 1600s
• First person to challenge the idea of
spontaneous generation
• Disbelieved the idea that flies would
magically be created from rotting
meat
• Designed a simple experiment to
disprove this
Redi’s Experiment
• Hypothesis: If a jar containing
rotting meat is covered, it will
produce no flies. The jar left
uncovered will produce flies .
• Experiment:
• IV-cover
• DV-presence of flies
Redi’s Conclusions
• Flies are produced from rotting meat only because the flies
lay eggs, they grow into maggots, and metamorphose into
flies (If flies can’t get to meat to lay eggs, no new flies will
be created)
• Meat doesn’t produce flies
Objections to Redi’s Experiment
• Redi’s claim that flies don’t spontaneously re-generate
was REJECTED!!!
• Why?
• “Sealing the jar closed prevented a magical essence
from entering the rotting meat and bringing it to life”
Lazzaro Spallanzani
• Italian scientist, 1700s
• Believed microbes in the air cause food spoilage and
they can be killed by boiling
• Designed an experiment to disprove that food produced
living microbes to cause spoilage
Spallanzani’s Experiment
• Hypothesis: If air is allowed to reach food, then microbes
will get in it and cause food spoilage
• Both flasks were boiled to kill any prior microbes
• Flask 1-uncovered (Spoiled)
• Flask 2-covered (didn’t Spoil)
Objections to Spallanzani’s Experiment
• Spallanzani’s Experiment was REJECTED!!!
• Why?
• “Sealing the flask shut blocked the entrance of a
magical life force in the air from getting to the broth
• (Few people had seen microbes, so few believed in
them)
Disproving a Magical Life Force
• A special experiment needed to be designed to disprove
the idea of a magical life force
• How?
• Louis Pasteur is going to improve Spallanzani’s
experiment
Pasteur
• French Scientist, 1800s (nearly 200 years later!!!)
• Invented pasteurization: sterilization by heat
• Pasteur’s Experiment:
• Hypothesis: If boiled broth is kept free of bacteria,
then it will not spoil even if air can reach it.
• Designed a special flask that would allow air to flow it,
but not allow microbes to fall/settle into flask
Swan-Necked Flask (S-Flask)
Curved neck allows air in, but prevents microbes in air
from settling into jar
Spontaneous Generation is Disproved
• Pasteur concluded that the food didn’t spoil because
microbes in air didn’t get to food, even though air was
allowed to flow in
• Pasteur is considered the “Father of Modern
Microbiology”
• Pasteurization (sterilization by heat) lead to preserving
foods with the canning process and eventually canned
goods at stores
How have discovery of cells impacted
humans?
• Hygiene:
• In the late 1870s, doctors start to wash hands and utensils
before surgery, some start to wear gloves!
• Joseph Lister invented Listerine because bacteria in mouth
cause bad breath
• Medicine:
• Understanding of medical diseases such as cancer
• Development of antibiotics and preventative disease measures
• Food:
• Use of refrigerators to keep foods longer
• Cover food dishes to keep microbes out