Name
Ms. Kellock
Science – Period
Date
Where Does Life Come From?
Life Comes From Life (Biogenesis)
Have you ever taken a walk after a thunderstorm and found earthworms all over the sidewalk?
People have noticed that earthworms are often found on the ground after rainstorms. It’s no wonder
that people used to think the earthworms had fallen from the sky when it rained. It was a logical
conclusion based on repeated experience. But was it true? Jan Baptist van Helmont wrote a recipe for
making mice by placing grain in a corner and covering it with rags. For much of history, people believed
that living things came from nonliving matter, an idea called the Theory of Spontaneous Generation or
Abiogenesis.
CONTROLLED EXPERIMENTS
People also believed that maggots grew from decaying meat. In 1668, Francesco Redi
(pictured at right) an Italian doctor, conducted one of the first controlled
experiments in science. A controlled experiment is one in which you change just one
thing to find out the result. Redi put meat into two groups of jars. He covered one
group with a cloth, but left the other jars open. The two groups and their contents
were the same, except for one thing: the cover on one set of jars. The results of the
experiment were that after a period of time maggots appeared on the meat in the open jar, but not on
the meat in the covered jar. This showed that maggots hatched from eggs that flies had laid on the
meat, not from the meat itself. Redi’s experiment is shown in Fig 1.
Fig 1 – Redi’s experiment
Uncovered jar with meat
Covered jar with meat
Chapter 2 Biogenesis
Flies around and in jar, maggots in jar and on meat
Flies around jar, no maggots in jar or on meat
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In the late 1700’s, Lazzaro Spallanzani designed an experiment that showed that tiny organisms
came from other tiny organisms in the air. He sterilized broth in two sets of flasks, sealing one group,
and leaving the other group open to the air. The open flask became cloudy with organisms. The sealed
flask developed no organisms. When he opened the sealed flasks, they then did become contaminated.
Spallanzani’s experiment showed that organisms from the air entered one flasks and not the other
because it was sealed, and it was the organisms from the air that grew in the broth. Spallanzani’s
experiment is shown in Fig 2
Fig 2 – Spallanzani’s experiment
Broth boiled, flask left open
Broth boiled
Open flask develops organisms
flask sealed
Sealed flask remains uncontaminated
Biogenesis
It was not until the mid-1800’s that Louis Pasteur, a French chemist, showed conclusively that
living things do not come from nonliving materials. In the experiment illustrated in Fig 3, Pasteur boiled
broth in flasks with long, curved necks. The broth remained uncontaminated for a long time. When dust
that collected in the curved neck of one flask was allowed to mix with the broth, the broth in that flask
became contaminated with bacteria. The work of Redi, Spallanzani, Pasteur, and others provided enough
evidence to finally disprove the Theory of Spontaneous Generation. This theory was replaced with
Biogenesis, the theory that living things come from other living things.
Fig 3 – Pasteur’s Experiment
Boiled
broth
Boiled broth exposed to air
Chapter 2 Biogenesis
Boiled broth exposed to air
Broth exposed to dust
broth remains uncontaminated
Broth shows bacterial growth
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Name
Ms. Kellock
Science – Period
Date
WHERE DOES LIFE COME FROM?
The Development of the Cell Theory
Pre-read the questions below, and then read the article about the experiments done by Francesco Redi, Lazzaro
Spallanzani, and Louis Pasteur. Use the information to answer the questions below.
1.
Define the following terms:
a. Spontaneous Generation/Abiogenesis
b. Biogenesis
c.
Controlled experiment
2. Summarize the results of Redi’s, Spallanzani’s, and Pasteur’s experiments. For each experiment - Write a
proper hypothesis, identify the control and experimental groups, identify the independent variable, and
write a conclusion.
Francesco Redi (early 1700’s)
HYPOTHESIS
EXPERIMENTAL
SET-UP
Control Group
Experimental
Group
INDEPENDENT VARIABLE
CONCLUSION
Chapter 2 Biogenesis
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Lazzaro Spallanzani (late 1700’s)
HYPOTHESIS
EXPERIMENTAL
SET-UP
Control Group
Experimental
Group
INDEPENDENT VARIABLE
CONCLUSION
Louis Pasteur (mid 1800’s)
HYPOTHESIS
EXPERIMENTAL
SET-UP
Control Group
Experimental
Group
INDEPENDENT VARIABLE
CONCLUSION
3. Explain how Pasteur’s results disproved the Theory of Spontaneous Generation.
4. State the Theory of Biogenesis
5. Which scientist – Hooke, Van Leeuwenhoek, Schleiden, Schwann, or Virchow – discovered the part of
the cell theory that supports Pasteur’s conclusion?
What did he observe that supported Pasteur’s conclusion?
Chapter 2 Biogenesis
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