1 – 2 How Scientists Work
How is Science Done?

Scientists use the scientific method. When scientists have a question about something in
the world they use this method to find an answer:
 State the Problem or Question
 Research
 State a hypothesis
 Design an experiment with a control
group, constants and variables
 Analyze data/ results
 Conclusion or Summary
 Publish Results
1. State the Problem or Question
 What have I observed?
 What do I want to know?
2. Research
 Has anyone asked this before?
 Did they discover an answer?
 How did they go about looking for an answer?
 What other things do I need to understand to answer my question?
3. Form a Hypothesis
 Based on the research you have done, write a possible answer or solution – your best
educated guess – to your question.
4. Design an Experiment
 ________________: Part of your experiment that is not varied in anyway. You
can compare your test groups to this set standard group.
 ____________________- The change/difference you make in the experiment (the
thing you are testing). Also called manipulated variable
 ____________________- The differences that result from the experiment, the
resulting effect. Also called responding variable.
 ________________- Things in the experiment that do not change, kept exactly
the same for each test group so they do not affect the results.
5. Data/Results
 It is easier to understand the data if it is put into a______________________.
 Make sure all data is clearly labeled. Charts and graph should always include units and
titles.
 When graphing the independent variable should be on the _______________and the
dependent variable should be on the ________________.
6. Analysis
 What happened?
 What was expected? What was unexpected?
 What trends did you notice in the data?
7. Conclusion or Summary
 Indicate whether or not the data supports the hypothesis and explain why or why not.
 Suggest possible improvements to the experiment.
 Suggest further avenues of research or uses for the information discovered.
Learning Checkpoint
 What are the steps of the scientific method?

In which step would you find charts and graphs?

What is the difference between an independent variable and a dependent variable?

What is the purpose of a control group?

What does it mean to have a controlled experiment?
An Example of Science at Work (1-2)
 Observed: sometimes organisms just “arose” from nonliving things: ex. maggots came
from meat.
 The Question: How do new living things come into being?
 Hypothesis: In some cases, nonliving objects can spontaneously generate living
organisms.
1st Experiment- 1668, Francesco Redi:
 Meat in _____________ and ________________ jars
 Proposed a new hypothesis: The maggots came from eggs left by flies on the meat that
were too small to see.
 Concluded: Maggots came from flies.
Figure 1-8 Redi’s Experiment on Spontaneous Generation
OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the
meat.
HYPOTHESIS: Flies produce maggots.
PROCEDURE
Uncovered jars
Covered jars
Controlled Variables:
jars, type of meat,
location, temperature,
time
Several
days pass
Manipulated Variables:
gauze covering that
keeps flies away from
meat
Responding Variable:
Maggots appear
No maggots appear
whether maggots
appear
CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous
generation of maggots did not occur.
Science continues...New Ideas with new discoveries
 New discovery!- tiny microorganisms (discovered by Anton van Leeuwenhoek)
2nd Experiment- Mid 1700s, John Needham:
 Repeats Redi’s experiment.
 His hypothesis: Spontaneous generation can occur
under the right conditions.
 Result: microorganisms appear in sealed flask of boiled gravy.
Science Experiments are always repeated:
3rd Experiment- Lazzaro Spallanzani:
 Thinks Needham did not boil gravy long enough to kill existing microorganisms.
 Results: When left exposed to air, microorganisms will appear in boiled gravy.
 He concluded that microorganisms could not come from gravy but appeared instead
from microorganisms existing in the air.
Figure 1-10 Spallanzani’s Experiment
Section 1-2
Gravy is boiled.
Flask is
open.
Gravy is teeming
with microorganisms.
Gravy is boiled.
Flask is
sealed.
Gravy is free of
microorganisms.
Needham tried
first but didn’t
bring gravy to
hot enough
temperature.
New Question: Is air the “life force”?
4th Experiment- 1864, Louis Pasteur:
 Set out to dismiss the notion that the “life force”, air was needed to generate life.

Used curved neck on flask so air could get in but organisms would not.
 Concluded that all living things can only come from living things.
 This has been tested over and over and is now considered a theory called ____________.
Figure 1-11 Pasteur’s Experiment
Broth is boiled.
Broth is free of
microorganisms
for a year.
Curved neck
is removed.
Broth is
teeming with microorganisms.
Learning Checkpoint
 Did all 4 scientists use good scientific thinking and a controlled experiment?

What is spontaneous generation?

What was the point of the “swan neck” Pasteur added to his flask?

What is biogenesis?