Grade 7 Science Review
Scientist
Hypothesis
Experiment
Conclusion
Francisco Redi
If flies could get to the
meat and lay eggs,
maggots would be
produced.
He tested meat in 3 different jars.
Proved that decaying meat
did not produce maggots.
1st jar- uncovered
- meat was exposed to the air
- flies were visible on the meat & jar
DISPROVED theory of
spontaneous generation
2nd jar- covered
- meat in the jar is not exposed to the air
- flies are visible on the cover of the jar but not
inside the jar on the meat
3rd jar- covered with netting
- the meat rotted
- no maggots
John Needham
Boiling broth would kill
all living things.
Conducted an experiment in which he placed a
broth into a bottle, heated the bottle to kill
anything inside, then sealed it.
Days later, he reported the presence of life in the
broth and announced that life had been created
from nonlife.
Big mistake: He didn’t heat the broth long enough
so both broths became contaminated.
Claimed to have proved
spontaneous generation
Lazzaro Spallanzani
Microbes come from
the air. Boiling will kill
microorganisms.
Placed broth in two separate bottles, boiled broth
in both bottles, then sealed one bottle and left the
other open. Days later, the unsealed bottle
contained small living things. The sealed bottle
showed no signs of life.
Boiling did NOT damage
broth’s ability to support
life, growth depended on
the SEAL only.
He put broth into several S-shaped flasks. Each
flask was boiled and placed at various locations. He
observed no life in the jar for one year. He then
broke off the top of the flask, exposing it to the air,
and noted life-forms in the broth within days.
He reasoned that the
contamination came from
life-forms in the air.
Disproved spontaneous
2 corrections he made: 1. boiled the broth and flask generation
longer 2. sealed both flasks so no air could enter
Louis Pasteur
Microbes come from
cells of organisms on
dust particles in the air;
not the air itself.
Disproved spontaneous
generation
Definitions
Spontaneous generation
The idea that living things can come
from non-living things
Controlled experiment
Very structured, always contains the
independent variable and dependent
variable
Biogenesis
The theory that living things come from
only other living things
Who discovered the microscope?
Anton van Leeuwenhoek
Theory
A full explanation of an event in nature;
subject to change
Microorganism/Microbe
Microscopic organism
Pasteurization
Sterilizing milk
Sterile
Free from bacteria, totally clean
Other Concepts to Know
1. What are variables in an experiment? Factors to be tested
2. How many variables should an experiment test at one time? 1
3. What is a controlled experiment? Experimenter controls the variable to be tested; you control the IV
4. How a theory can be replaced or written – by interpreting existing data in new ways and including those views with new results
5. Identify the IV, DV & constant variables in an experiment.
6. Why did scientists in the 1800s use direct observation?