Download 4. What was the variable in Fleming`s experiment?

Name ________________________________ Date __________________ Period ___
The Scientific Method
In 1928, Sir Alexander Fleming was studying Staphylococcus bacteria grown in petri dishes.
He noticed a mold called Penicillium also growing in some of the dishes. A “clear zone”
existed around the mold because all the bacteria that had grown in this area had died. In the
culture dishes without the mold, no clear area existed.
Fleming reasoned that the mold must be producing a chemical that killed the bacteria. He
decided to isolate this substance and then test it to see if it would kill bacteria. Fleming
transferred the mold to a nutrient broth solution. This solution contained all the materials
the mold needed to grow and reproduce. He allowed the mold to grow in the nutrient broth
for a while, and then he removed the mold from the broth. Fleming then added the nutrient
broth in which the mold had grown to a culture of bacteria he had grown in a petri dish. He
observed that the bacteria died, leaving a clear zone in the bacteria. Fleming then added
nutrient broth that had not had mold growing in it to another dish of bacteria. Bacteria in this
dish were not killed. Fleming concluded that mold produced a bacteria-killing substance in
broth. He called the substance that killed bacteria “penicillin”, the very first antibiotic
discovered.
1. Identify the problem Fleming wanted to solve. ________________________________________________
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2. What was Fleming's hypothesis? ____________________________________________________________
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3. How did Fleming test his hypothesis? ______________________________________________________
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4. What was the variable in Fleming's experiment? _________________________________________
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5. What was the control? _____________________________________________________________________
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6. What data did Fleming obtain? ____________________________________________________________
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7. What was his conclusion? ___________________________________________________________________
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Name_________________________________ Date_______________________ Class period_________
The Scientific Method, continued
Part 1: In your textbook, read about observing and hypothesizing.
Answer the following questions.
1. What is meant by scientific methods? _________________________________________________
2. What is a hypothesis? ______________________________________________________________
3. How is a hypothesis tested? _________________________________________________________
Part 2: In your textbook, read about experimenting.
For each item in Column A, write the letter of the matching item in
Column B. Column A
Column B
a. dependent variable
____________ 4. A procedure that tests a hypothesis by collecting
information under controlled conditions
____________ 5. In an experiment, the group in which all conditions
are kept the same
b. experimental group
c. independent variable
d. experiment
____________ 6. In an experiment, the group in which all conditions
are kept the same except for the one being tested
e. control group
____________ 7. The condition that is changed by the experimenter
____________ 8. The condition being observed or measured in
Part 3: Use each of the terms below just once to complete the passage.
experimental results
experiment(s)
hypothesis
scientific journals
theory
valid
laws
verify
When (9) ___________________________ are reported in (10) _______________________ other
scientists may try to (11) ______________________ the results by repeating the (12)
_________________________. Usually when a(n) (13) _________________________ is supported by
data from several scientists, it is considered (14) ________________________ . Over time, a hypothesis
that is supported by many observations and experiments becomes a (15) ______________________ .
Some well-established facts of nature, such as gravity, are recognized as (16) ____________________ .