Name/Date: ________________________
The Scientific Method
Introduction
Each of the fields of science seeks to better understand the world around us. Given the right hypotheses, proper
experimentation, and enough data, all phenomena that occur in the natural world are explainable. In order to
encourage the exchange of ideas and to minimize mistakes, scientists each follow the same basic sequence in
conducting their research.
This lab will familiarize you with this sequence, called the scientific method. You will apply each of the steps in
the scientific method, using data from real-world scenarios.
Background
The scientific method is divided into these steps:
1. Question – What is the unexplained phenomenon?
2. Hypothesis – A testable, falsifiable explanation of the phenomenon. The hypothesis is based on
observations, or information gathered by sight, sound, smell, or touch.
3. Experiment – A set of procedures that seeks to collect data and test the hypothesis.
a. Data Analysis – Measurements taken from an experiment are examined graphically for patterns.
b. Conclusion – Patterns in the data are compared to the predictions within the original hypothesis.
The scientist determines whether the supports the original hypothesis, or whether it must be rejected.
4. Collaboration – Experimental procedures, results, analysis, and conclusions are shared with other scientists
in the same field. The experiment will be repeated to look for errors or bias.
Observation and Hypothesis
While scientists and philosophers of ancient Greece and Rome witnessed the growth of seeds into plants, the
hatching of eggs, and the life birth of mammals, not all living things appeared to arise from these methods. The
Greek philosopher Aristotle, in his book entitled The History of Animals, stated,
“So with animals, some spring from parent animals according to their kind, whilst others grow
spontaneously and not from kindred stock; and of these instances of spontaneous generation some come
from putrefying earth or vegetable matter, as is the case with a number of insects, while others are
spontaneously generated in the inside of animals out of the secretions of their several organs.”
This gave rise to the idea of spontaneous generation. Aristotle, along with many other scientists, believed that
life could arise from non-living matter. This theory become so widely accepted that it lasted for about 1,500
years! Some scientists even had developed “recipes” for creating life. One example involved placing soiled
garments and wheat into a large jar for 21 days in a dark room. Mice would often be found inside the jar after
the 21 days had passed.
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1. Identify the initial question in this example.
2. What hypothesis was made in relation to this question?
3. What observations were made by Aristotle and other scientists that served as the basis for the
hypothesis?
4. Spontaneous generation was eventually accepted as a scientific theory for hundreds of years. How are
theories different than hypotheses?
Identifying a Testable Hypothesis
As a skeptical scientist, you are interested in testing and verifying the claims of spontaneous generation. Which
of these would be considered a testable, falsifiable hypothesis that could become the basis of an experiment?
5. Life can arise from non-living matter. ( Testable / Not testable )
Why? __________________________________________________________________________
6. Maggots will spontaneously arise when a piece of uncooked meat is left exposed to air during the spring
and summer months for at least 7 days.
( Testable / Not testable )
Why? __________________________________________________________________________
7. A fungus will spontaneously appear when a piece of bread or cheese is left exposed to warm, humid air
for at least 3 days. ( Testable / Not testable )
Why? __________________________________________________________________________
8. Rats can be spontaneously created from wheat. ( Testable / Not testable )
Why? __________________________________________________________________________
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Experimental Design
Louis Pasteur conducted a famous experiment in 1864 to disprove this theory. He took
containers of broth and boiled them for several minutes. He used two different types of
glass flasks. One type had a long S-shaped neck. The other had a straight neck. The
broth was then allowed to cool and remain at room temperature for several days.
Subsequently, the flasks with the S-shaped necks were found to be unchanged. The
original smell, color, and clarity of the broth were all present. The flasks with the
straight neck were found to be cloudy with a foul, unpleasant smell.
9. Pasteur designed his experiment with a control group and an experimental group. What is the
purpose of each of these groups? Identify which flasks were the control, and which were the
experimental group.
10. What data was collected in this experiment?
11. In his conclusion for this experiment, Pasteur wrote, “Never will the doctrine of spontaneous generation
recover from the mortal blow of this simple experiment.” Is this a reasonable conclusion given the
results of his experiment?
Data Analysis and Conclusion
In the 17th century, many believed that trees and other plants gained their mass from
absorbing nutrients from the soil. To test this idea, Johannes Baptista van Helmont
conducted an experiment in 1648. He planted a small willow seedling in a large pot. He
measured the initial mass of the tree and the initial mass of dry soil. He added distilled
water to the tree as the soil became dry. After five years, measured the tree’s mass and the
mass of the dry soil again.
12. This is considered to be one of the first recorded quantitative experiments in
biology. What is quantitative?
13. This data table represents some of the data that may have been collected from van Helmont’s
experiment:
Initial Mass of
Willow Tree
5 pounds
Initial Mass of
Dried Soil
200 pounds
Final Mass of
Willow Tree
170 pounds
Final Mass of
Soil
199.8 pounds
14. As a conclusion from his experiment, van Helmont wrote that the increase in the tree’s mass must have
come from it absorbing water. Does this seem like a valid conclusion from the data?
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15. Where did the added mass of the tree actually come from?
16. Why was van Helmont’s conclusion incorrect? What variables were not accounted for as matter moved
from the environment into the tree?
17. Would you consider this experiment a success or failure? Explain your reasoning.
18. Why is so important for scientists like van Helmont to publish the full procedure and results of their
experiments, instead of simply announcing their conclusions to the public?
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