Travis Miller BIO 102-35
Lab Exercise 1
Review of the Scientific Method
OBJECTIVES:
1. Define the terms hypothesis, independent variable, dependent variable, control group and
experimental group.
2. Describe the steps of the scientific method.
3. Utilize the scientific method when analyzing information and conducting experiments.
INTRODUCTION:
The scientific method illustrates how scientists approach questions and problems, how they
propose answers and solutions and how they test whether their answers and solutions are valid.
The scientific method is usually presented as a series of steps, which helps to simplify the
process of "how to do" science. Please understand that the scientific method is essentially a guide
and scientists may not rigidly follow each and every step. The scientific method can be modified
in use and still test possible answers or solutions.
You will first read through and re-familiarize yourself with the usual steps of the scientific
method. Next, you will contemplate a scenario and sketch out steps that a scientist could follow
to address it. Then you will answer questions associated with the scenario. By the end of this
exercise, your familiarity with the scientific method will be refreshed, which will help you to get
ready to tackle the rest of the semester!
PROCEDURE: Complete parts A, B, C, and D below. Parts A, B, and C, and D
have questions for you to complete. PLEASE HIGHLIGHT YOUR ANSWERS
IN YELLOW, OR WRITE THEM IN RED.
Part A. Steps of the Scientific Method:
Read through the typical steps of the scientific method and think about them! After reading part
A, answer the questions at the end of Part A.
The scientific method includes:
1. Making observations: Science begins with observations of the natural world. These
observations are typically precise and detailed. For example: "When iodine is mixed
with potato juice, the iodine turns blue-black in color. When iodine is mixed with
onion juice, it does not turn blue-black in color."
2. Asking questions: Questions about the observations usually occur almost as soon as the
observations are made. For example: "Why does iodine change color when mixed
with potato juice?"
3. Proposing hypotheses: A scientific hypothesis (singular form of the word "hypotheses")
is a possible answer to the question asked. In other words, a hypothesis is an "educated
guess", and this is because scientists do background research before proposing
hypotheses. Background research usually involves becoming familiar with published
material and communicating with others who are experts in the area related to the
question. For example: "Potatoes contain a polysaccharide known as starch and
onions contain monosaccharides like glucose and sucrose" is information that has
been published in many textbooks and journals. By knowing this background, you
may create a hypothesis that states "Iodine changes color when exposed to starch,
but does not change color when exposed to other sugars."
a. A hypothesis must be testable and falsifiable to be of scientific use. If a
hypothesis cannot be tested in any way and cannot be potentially proven false,
then it is not something that can be evaluated scientifically. Because it must be
testable and falsifiable, it must use processes known to occur in nature. So, we
can't use supernatural explanations in a scientific hypothesis. That doesn't
necessarily mean they're wrong—maybe the world is full of ghosts, demons, God,
and so forth; but there is no way to test these hypotheses and prove them wrong,
so they can't be evaluated for scientific "correctness." Thus they lie outside the
realm of science.
b. For example, suppose your grandmother goes out to the cemetery to put flowers
on your grandfather's grave and falls over dead. You could hypothesize that she
died of a stroke or heart attack, and this hypothesis could be tested by an autopsy,
which would show the cause of her death. You can't hypothesize that a ghost
came out of the ground and scared her to death—that explanation can't be tested,
so it isn't scientific.
4. Making a prediction: Using the hypothesis for guidance, a prediction states what should
occur if the hypothesis is valid. A prediction is also known as the "if-then statement" For
example: "If iodine changes color only when exposed to starch, then it will not
change color when exposed to carbohydrates like glucose and sucrose."
5. Testing the hypothesis and prediction: Testing a hypothesis and prediction can be done
by several different mechanisms and, at times, a combination of these different
mechanisms is used. Hypotheses can be tested by making comprehensive observations,
by using models and by performing experiments.
a. Comprehensive observations: observations of the same aspect of nature in as
many ways as possible.
b. Models: systems that act as analogies to test an aspect of nature that has not yet
been directly observed.
c. Experiments: tests that simplify the conditions under which observations are
made. Good experiments have certain characteristics:
i. They test variables, which are factors that can change in value under
different conditions. Usually, scientists manipulate an independent
variable to measure its effect on a dependent variable. It is easiest to
think about independent variables as the ones that are controlled by the
scientist and the dependent variables as the ones that are observed and
measured. A dependent variable may be influenced (may change) because
of the independent variable, but it is not intentionally altered or
manipulated by the scientist. An experiment should only have one type of
independent variable and one type of dependent variable at a time. For
example: "Different types of carbohydrate solutions will be mixed
with iodine. The color change of iodine will be observed." In this case,
the carbohydrate solutions collectively are the independent variable (they
are controlled by the scientist) and the color change is the dependent
variable.
ii. Experiments should contain control groups and experimental groups.
Experimental groups contain the variable being tested. Control groups are
similar in all ways to the experimental groups and treated the same way,
except control groups lack the variable being tested. Control groups act as
a standard of comparison for experimental groups. They are needed to
ensure the independent variables are causing the dependent variable to
change, rather than some unknown factor. For example: The carbohydrate
solutions used in the iodine experiment are the experimental groups since
they contain some type of carbohydrate to be tested. A control group
would be a solution of everything but a carbohydrate to be tested.
iii. Results (also called data) obtained from experiments should allow a
scientist to definitively support or reject the hypothesis.
6. Analyzing the results of the test: Data that confirm the prediction support the
hypothesis. Results that do not fit the prediction indicate the hypothesis may be flawed.
7. Repeating the test: Conclusions regarding the question or problem under study should
not be generated based on one single test. Unknown factors may have affected the test
and, therefore, may have affected the results. If the test is repeated many times and the
results are basically the same with each repetition, the results are more likely to be valid.
8. Reporting results and conclusions drawn from them: If scientists did not report their
findings and the conclusions they have generated, then science would not be progressive
as no one would know what others were doing! Scientists publish their findings in
scientific journals for others to critically analyze the work. This analysis often includes
other scientists attempting to replicate the same kinds of tests to see if they too can
achieve similar results. If many scientists within the same field achieve similar results
using similar tests on the same proposed hypothesis, then the hypothesis is more
supported and less likely to be invalid.
Part A Questions:
1. When researchers start to investigate a question, using scientific method, what is the
first thing they do?
They make observations.
2. After making observations, the scientists form a hypothesis. What two criteria must a
good hypothesis meet in order to be of any scientific use?
A hypothesis must be testable and falsifiable.
3. After forming a hypothesis, the scientists form a prediction. What purpose does a
prediction have in regards to the scientific method?
A prediction serves to state what should occur if a hypothesis is valid.
4. When conducting a test, why is it important to repeat the test many times?
Unknown factors may have affected the test and therefore affected the results.
Repeating the test reduces the chance of those unknown factors occurring numerous
times, making the results more reliable.
5. Why does a scientific experiment need a control group?
The control groups lack the tested variable, giving the experiment a baseline and
acting as a "standard of comparison" for the experimental groups. This standard of
comparison allows us to see if the independent variables are causing the dependent
variable to change instead of an unknown factor.
6. How does a control group differ from an experimental group?
A control group lacks the tested variable; an experimental group includes the tested
variable.
7. What is the difference between an independent variable and a dependent variable?
An Independent variable is a variable that the experimenter controls, while a
dependent variable is one observed and measured (often influenced by changes in
the independent variable).
Part B. Using the Scientific Method to Analyze a Scenario
Here is your challenge: Read the scenario below and use what you know of the scientific
method. You need to think like a scientist and provide answers to the questions associated with
the scenario.
Scenario:
In 1993, a new disease emerged in the Pacific Northwest region of the United States. The disease
produced symptoms including watery eyes, nasal congestion, fever and a bright green color that
appeared on the outer region of the ears. The disease was termed "Green Ear Disease"
(sometimes medical science is not all that creative!). Shortly after hundreds of people, all of who
were snowboarders, come down with the disease, it was discovered that they all had been
exposed to a new species of bacteria that is now called Staphylococcus verdephia. A group of
scientists with the Centers for Disease Control and Prevention (CDC) became interested in trying
to find a treatment for this infection. They first performed a great deal of background research on
different Staphylococcus species that were similar to Staphylococcus verdephia. They also
examined the antibiotics that were typically used to treat the other, known Staphylococcus
species. The group found that an antibiotic known as Staphylostopitnow was effective in treating
many Staphylococcus species and decided to try it on Staphylococcus verdephia, the likely
causative agent of Green Ear Disease.
Questions to Answer:
1. What is the main question being examined in the scenario?
Will Staphylostopitnow effectively treat Staphylococcus verdephia?
2. Construct a hypothesis for this scenario (act as if you are one of the CDC researchers!)
and write it below.
Staphylostopitnow will effectively treat Staphylococcus verdephia because of its
effectiveness in treating various Staphylococcus species.
3. Using your hypothesis as a guide, create a prediction. (Remember, a prediction is an "if,
then" statement.)
If Staphylostopitnow effectively treats Staphylococcus verdephia, a lower bacterial count of
Staphylococcus verdephia or the elimination of said bacteria should be observed after the
introduction of Staphylostopitnow.
4. Describe, in as much detail as possible, how you could test your hypothesis. Include any
factors that you think would need to be considered.
An antibiotic works by disrupting the bacterial process; therefore, it should be observed
that the bacteria will slow down in its growth rate or die off if the antibiotic is effective. For
this experiment, it will be vital to set up multiple strains of Staphylococcus and possibly
strains of bacteria known to be resistant to the antibiotic and the testable strain
(staphylococcus verdephia), then record what the antibiotics do to each strain. Having
groups of each bacteria without antibiotics will allow a baseline of how the bacteria grow.
Then the strains with antibiotics introduced can be compared to the baseline to see if the
bacterial process slowed, stopped entirely, or had no effect. When designing the
experiment, it is essential to keep all variables the same in terms of bacterial environment,
amount of the bacteria, amount of the antibiotic, time passed, and repeat said experiment
multiple times to ensure validity. The importance of having strains known to be treated by
the antibiotic will help ensure the antibiotic is working correctly and is not an ineffective
batch.
5. For the experiment you just described, list what the independent variable is and what the
dependent variable is. What type(s) of control group(s) would be needed?
The independent variable will be the tested bacterial strain, while the dependent variable
will be the bacterial count after the addition of the antibiotic. For control groups, it will be
essential to have several staphylococcus strains where interactions between the antibiotic
(Staphylostopitnow) and the bacterial strain are known, and possibly a strain known to be
resistant to the antibiotic and observe these strains without the introduction of any
antibiotics to grow. These groups will give a baseline of bacterial counts to compare to the
experimental groups (the same strains with the antibiotic introduced) and aid in the
determination of the effectiveness of the antibiotic.
6. If the experiment were to be conducted, what results would you expect to see if the
original hypothesis was supported? Explain your answer.
Based on the mechanism of how an antibiotic works by disrupting the bacterial process,
one would expect to see lower bacterial counts of Staphylococcus verdephia if the antibiotic
is effective. At the same time, the control groups would follow predicted bacterial counts
from unimpeded growth.
7. Considering the scenario you just worked with, what other pieces of information would
have been useful to know before trying to create an experiment to test your hypothesis?
Other information that would have been useful is how similar this new strain is to specific
strains of Staphylococcus, and if there is a more effective treatment to a specific strain of
Staphylococcus that shares more similarities with the newly discovered strain. If so, it may
have been worth creating another experiment testing another treatment's efficacy and
comparing the treatments on the new strain.
8. What part of working with the scenario was easiest? Why was that part easiest? What
part of working with the scenario was more difficult? Why was that part more difficult?
The easiest was creating the question from the scenario. It was clearly laid out what the
intent of the scenario was. The most challenging part was deciding what information could
have been more helpful, as the "background research" could cover so many variables that
are not mentioned, making the statement quite vague.
Part C: Design an Experiment
You observe that plants don't grow in caves and decide to test the hypothesis that "plants need
light to grow." Your prediction is "If I grow some plants in the light, and some plants
in the dark, then only the plants in the light will grow."
1.
What will be the experimental group for your test?
The plants grown in the absence of light.
2. What will be the control group for your test?
The plants grown in the presence light.
3. What will be the independent variable?
The amount of light given to each plant.
4. What will be the dependent variable?
The growth of the plant.
5. What result will you see for your experiment if your hypothesis is
supported?
It should be observed that the plants in the presence of light will grow, while plants in the
absence of light should not have any growth.
Part D: Scientific Theories
A scientific hypothesis can potentially become a scientific theory. Now, the common
concept of "just a theory" dismisses a theory as wild speculation. It's a major source of confusion
between scientists and non-scientists. A scientific theory is the diametric opposite of "just a
theory." To become a scientific theory, an explanation must be supported by large amounts of
evidence and withstand multiple tests by many researchers. Scientists love to prove each other
wrong, so if there's a hole in a hypothesis or theory, someone will find it.
Some examples of scientific theories:
 The germ theory of disease: diseases are caused by microorganisms. Today we
accept that you should always wash your hands after using the bathroom, after
carrying out the garbage, before eating, before treating an injury, before helping a
woman give birth, etc. But when Louis Pasteur first proposed the germ theory of
disease in the 1800's, it was widely ridiculed. The idea that something so small
you can't see it could make you sick seemed absurd. The head of the French
Academy of Science dismissed the germ theory as "ridiculous fiction". So it's not
the approval of other scientists that validates a theory; it's the testing and
evidence. (We might also note that we now know not all diseases are caused by
microorganisms; there are illnesses that result from environmental factors, ones
that are genetically based, etc. That doesn't make germ theory wrong — it just
doesn't apply in all cases.)
 The theory of evolution by natural selection: all species are related, and allele
frequencies of a population change over time because heritable traits cause some
individuals to have more offspring than others.
Fill in the blanks:

The cell theory, which you covered in Bio 101, states that all organisms are made
up of _________cells_________________________, and new cells come only
from _______pre-existing cells______________________________..