Transcript Designing a Controlled Experiment

The scientific method:
1.
2.
3.
4.
5.
Asking a question
Doing background research
Constructing a hypothesis
Testing the hypothesis with an controlled experiment
Analyzing the data & drawing a conclusion
- Was the hypothesis correct?
6. Sharing results
Transpiration experiment
Many years ago, people wanted to know how living things
came into existence.
?
They observed that maggots (fly larvae) appeared “suddenly”
on uncovered meat, and that frogs came from puddles.
Maggots appeared on
uncovered meat.
Frogs appeared in
puddles.
Why might people have believed that these animals arose
from nonliving material?
No microscopes yet.
They though baby turtles were created from wet sand.
They really did.
Spontaneous generation is the belief that life can come from
nonliving things.
According to this theory, maggots
“come from” meat.
Aristotle believed in
spontaneous generation!
Spontaneous = sudden
Generation = creation (genesis)
Redi had different hypothesis: that flies produced the
maggots. He disproved spontaneous generation.
How Redi disproved spontaneous generation
Redi tested his hypothesis using a controlled experiment.
In a controlled experiment, only ONE variable is changed.
All other variables are controlled (kept the same).
Which variable in Redi’s experiment was changed?
Gauze covering
Which variables in Redi’s experiment were controlled?
Size/type of jar, size/type of meat, location of jar, temperature
The variable that is changed is called the manipulated
variable.
How many manipulated variables are in a controlled experiment?
One
What was the manipulated variable in Redi’s experiment?
Gauze covering
The variable that is measured is called the responding
variable.
What was the responding variable in Redi’s experiment?
The maggots
In a controlled experiment, only one variable is changed to
ensure that the response was caused by that change.
Would Redi have gotten the same results if he had also put
different types of meat in each jar?
Redi recorded data by counting the number of maggots that
appeared in each jar.
Day 1
Day 2
Day 3
Day 4
Redi’s Data Table
Number of Maggots in Number of Maggots in
Covered Jar
Uncovered Jar
0
0
0
1
0
3
0
12
What was Redi’s hypothesis?
That maggots came from flies that landed on the meat.
Based on the data he collected, was Redi’s hypothesis correct?
Yes!
Graph Showing Redi’s Results
Number of Maggots
1. Labels
Time (Days)
Time should be shown on the X-axis
Graph Showing Redi’s Results
Number of Maggots
1. Labels
Time (Days)
Time should be shown on the X-axis
Graph Showing Redi’s Results
Number of Maggots
2. Data Range
Time (Days)
Data Range: Lowest and Highest Values
Graph Showing Redi’s Results
Number of Maggots
3. Key
Time (Days)
Redi’s experiment was significant because it provided
evidence against spontaneous generation.
Despite his solid experimental data, Redi was continually
attacked by other scientists who were supporters of S.G.
As scientific tools (such as microscopes) improved, the S.G.
hypothesis was finally discarded.
The controlled experiment – used by Redi 300 years ago – is
now the standard way to conduct a scientific investigation.