Transcript What is Science?

1-2: How Scientists Work
Essential Question:
1. How do scientists know what they claim
to know?
2. How does a scientific theory develop?
In the days before refrigeration….
….maggots were commonly found on spoiled food
Spontaneous generation = idea that living things
arise from non-living things….
Mice on grain
Maggots on meat
1. Why is Redi’s experiment on spontaneous generation
considered a controlled experiment?
• Redi kept all variables but one the same: covering
the jar.
Vocab
one variable changed at
• Controlled experiment = only _______
a time.
changed
• Manipulated variable = the one thing that is _________.
• Responding variable = the thing(s) that are measured as
manipulated variable.
response to _________________
same to make
• Controlled variables = things kept the __________
sure we have fair test.
2. How does a scientific theory compare with a scientific
hypothesis?
• Hypothesis = educated guess, possible explanation for small
set of observations. “iffy”
Ex – earthworms attracted to fertilizer
• Theory = well-tested explanation for big range of
observations. Not “iffy”
Ex – plate tectonics, evolution
3. How do scientists today usually communicate
their results and conclusions?
Usually publish report in scientific journal so other
scientists can review, look for mistakes, and repeat
to see if they get same results.
4. How did the design of Pasteur’s flask help him
successfully refute the hypothesis of
spontaneous generation?
• Curved neck allowed air in, but not microorganisms.
Showed living things come from other living things.
5. Evaluate the impact of Pasteur’s
research on both scientific thought
and society. What was the effect of
Pasteur’s investigation on scientists’
ideas and people’s lives?
• Disproved hypothesis of spontaneous
generation for good.
• Showed infections caused by
microorganisms (tiny living things).
• All milk you buy is pasteurized to kill
bacteria.
Writing in Science. Write a paragraph in which you analyze,
review, and critique the spontaneous generation hypothesis.
Questions to consider: What observations did the hypothesis
account for? Why did it seem logical at the time? What
evidence was overlooked or ignored?
Spontaneous generation explained why maggots
appeared on meat. It made sense at the time
because they didn’t seem to be coming from
anywhere else. What they overlooked was the
possibility that maggots were coming from fly
eggs too small to see.
1. What does it mean to be alive?
2. What makes living things different
from non-living?