SCIENTIFIC METHOD
Page 1-1
SCIENTIFIC METHOD AND DATA INTERPRETATION
Adapted by Robin Gibson-Brown for Distance Education from:
Bres, M. and Weisshaar, A., Thinking About Biology, p. 1-21.
Dickey, J., Laboratory Investigations for Biology, p. 1-28.
Hix, J.E., Introduction to FutureBasic for the Macintosh and Data Analysis, p. 80-89.
Woodcock, J., Concise Guide to Microsoft Works, p. 87-131.
OBJECTIVES
Following this laboratory, the student will be able to:
 understand the basic elements of the scientific method and apply this process to solving
problems.
 define and provide examples of the five stages of the scientific method.
 understand the importance of the three criteria used when setting up appropriate experiments.
 identify the three types of variables found in an experiment.
 list limitations and challenges to the scientific method.
 relate scientific method to environmental agencies and organizations.
 identify the components of tables and graphs.
 given a set of data, describe how it would best be presented.
 interpret graphs.
 use pencils and graph paper or computer software programs to generate tables and graphs.
MATERIALS




pencil
calculator
computer for graphing
graph paper (provided in this document)
LAB EXERCISES ONE (Pages 1-6)
The scientific method is a particular way of answering a question. It cannot be applied to all
questions. Answerable questions meet specific guidelines; specifically, they can only be
answered yes or no. In addition, the scientific investigations used to determine the answer to
these questions must be conducted following certain rules. When an investigation or experiment
is designed properly and meets these guidelines, the results are accepted by other scientists and
added to the existing body of scientific knowledge. If the experiment was not performed
according to specific guidelines, the results cannot be validated by other scientists.
The purpose of such guidelines can be understood by comparing them to sports records. For
example, a new record set in track and field event only counts if the meet was approved by the
governing body that sets the guidelines. The site and equipment used are scrutinized to insure
that they are within the regulations, and the athlete is tested for use of illicit substances. Only
when these required conditions are met is the record certified as valid.
SCIENTIFIC METHOD
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There are five steps in the scientific method. They are:
1. Make an OBSERVATION.
2. Formulate QUESTIONS.
3. Develop a HYPOTHESIS.
4. EXPERIMENTATION.
5. Interpret data forming CONCLUSIONS.
Observations are collected at the beginning of an investigation and lists of conditions are
identified that are associated with this observation. Based on these observations, specific
questions are formulated in an effort to learn more about this topic, for instance, what is it,
where/when does it occur, or how does it happen? Next, a hypothesis is formulated that
explains the findings in steps 1 and 2. A hypothesis is a tentative theory or intelligent guess. It
is NOT a proven fact, but a prediction that can be tested. In order to be useable, it must be
possible to disprove a hypothesis through experimentation. Experimental testing is used to
establish the validity of a hypothesis. There are three criteria used to set up an appropriate
experiment; they are:
1. THE RIGHT EXPERIMENT - the experiment must test all aspects of your hypothesis.
2. CONTROLLED EXPERIMENT - all experiments must be conducted using two groups,
a control group and an experimental group. In the control group, all variables are
constant. In the experimental group, all variables are constant EXCEPT the one being
tested. A variable is something that may change during the course of an experiment.
There are three types of variables:

The independent variable is manipulated by the experimenter and indicates the
condition or event under study.

The dependent variable may change due to the presence of, or change in, an
independent variable and measures the effect of changes caused by the independent
variable.

The controlled variable is a condition that could affect the outcome of an experiment
but does not because it is held constant by the experimenter.
3. REPRODUCIBLE - in order for a hypothesis to be accepted, the result must be
repeatable.
Finally, conclusions are drawn from the data collected that either support or dispute the
hypothesis. An underlying characteristic of the scientific method is its cyclical nature; it is a
process that is repeated as more information is obtained. In other words, the original conclusion
must be reevaluated when more information is received in order to determine if the hypothesis is
still valid.
SCIENTIFIC METHOD
Page 1-3
There are a number of challenges and limitations to the scientific method. When interpreting
results, there may be an insufficient number of experimental subjects available to effectively test
the hypothesis. Unexpected or multiple conclusions can also be generated that may not provide a
definite answer. In addition, observations and experimental results may be misinterpreted by the
experimenter, or it may be difficult to maintain objectivity in drawing conclusions based on
personal biases.
The scientific method can also be applied unethically as in the example of Edward Jenner, the
man who developed the small pox vaccine at the end of the eighteenth century. He tested this
vaccine on a child living in an orphanage by first giving him the vaccine and then infecting him
with a deadly strain of small pox. Thankfully, this experiment had a positive outcome. This
raises a question about drug testing on AIDS patients. One group is given the drug that could
potentially save or prolong their life while the other is given a placebo in an effort to determine
the efficacy of the drug. The groups are unaware of which substance they are taking. Is this an
ethical practice? Is it a necessary practice?
Sometimes, unexpected results are encountered as was the case in the experiments that disproved
the popular theory of spontaneous generation in the mid-seventeenth century which stated that
living organisms originated from non-living matter. A theory is a set of scientific assumptions
and explanations consistent with one another and supported by a large body of evidence which is
not fully proven. In support of the theory of spontaneous generation, it was noted that maggots
would appear on decaying meat that eventually turned into flies. The hypothesis: life originates
from nonliving material. Redi, an Italian physician, conducted the first experiments to
eventually disprove this theory by isolating meat in closed flasks and opened flasks. Maggots
appeared in a few days only in the open flasks which were exposed to flies that would lay their
eggs on the meat, an observation that escaped people initially. Further demonstrations, however,
were required to finally disprove this popular theory. When a theory is supported by an
overwhelming body of evidence, such as the work proving that life must originate from life or
Newton’s work regarding gravity, it is called a law.
Another limitation of the scientific method, or perhaps a blessing depending on your point of
view, is the discovery of many facts or products by accident. Take the case of the discovery of
penicillin by Alexander Fleming in 1928. He discovered clear patches on a Petri plate that had
previously been covered by disease-causing bacteria after it was accidentally left uncovered.
Fleming concluded that contaminants from the air had stopped the growth of bacteria. With the
help of other scientists, it was finally determined that an airborne mold produced a chemical,
named penicillin, which prevented the growth of certain types bacteria. This accidental
discovery provided the basis for the development of antibiotics used to treat many diseases, some
life-threatening.
SCIENTIFIC METHOD
Page 1-4
In this section of the lab the student will read the exercises and explore the details and
applications of the scientific method. Fill in the appropriate information as requested, and use
complete sentences when necessary to full explain you answer.
Scientific Method
Using the definitions provided, identify the correct step of the scientific method that corresponds
with the sentence below:
a. observation
b. question
c. hypothesis
d. experiment
e. conclusion
1. ______
Plants grown under red light will grow faster than those under white light.
2. ______
Maria’s experiment showed that chicken eggshells are more resistant to crushing
when the hens are fed extra calcium.
3. ______
There is no hot water in the kitchen sink or in the shower.
4. ______
Tanya grew bacteria from her mouth on special plates in the laboratory. She then
placed drops of different mouthwashes on each plate.
5. ______
If acid rain affects the plants of a particular lake, what affects are experienced by
animals that live in the same water?
Observations and Questions
You have been awarded a $50,000 grant to study the environmental preferences of Armadillium,
an arthropod (bug) that belongs to the class Crustacea. They are more commonly known as
pillbug, roly-poly, or sowbug. Based on your observations of where they are typically found,
under rotten logs or rocks, develop three questions that will be the basis for your experiments.
These questions will be used to prove your hypothesis so phrase them as follows for now: Do
roly-polies prefer _________ or ___________?
1. ___________________________________________________________________________
___________________________________________________________________________
2. ___________________________________________________________________________
___________________________________________________________________________
3. ___________________________________________________________________________
___________________________________________________________________________
SCIENTIFIC METHOD
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Forming a Hypothesis
Based on the questions you identified in the previous exercise, list your three hypotheses based
on their environmental preferences. The hypotheses must be testable and possible to disprove, so
phrase the sentence so it can be “answered” in either a positive or negative manner, for instance,
“Armadillium prefer …” or “Roly-polies avoid …”.
1. ___________________________________________________________________________
___________________________________________________________________________
2. ___________________________________________________________________________
___________________________________________________________________________
3. ___________________________________________________________________________
___________________________________________________________________________
Testing a Hypothesis
Some hypotheses can be tested by observation only, but more often, you will need a combination
of observation and experimentation to be sure about the accuracy of your results. To understand
how scientists work, you must follow the steps of the scientific method as they are used in actual
experiments.
In the following activities, you will see how the scientific method is used to set up experiments
and analyze the information (data) that is collected.
PROBLEM: Investigate the effects of fertilizer on plant growth.
First, a hypothesis is formed in order to predict what you think will happen, for instance:
HYPOTHESIS: Adding fertilizer will make plants grow taller.
Note how this statement can be proved or disproved
Next, an experiment is designed that compares the growth (in height) of plants that receive
fertilizer with those grown without fertilizer. It is set up as follows (FILL IN THE BLANKS
WITH THE APPROPRIATE TERMS):

Begin with 20 plants (same size and type) planted in the same size pots with the same
amount and type of soil, placed on a windowsill with the same light exposure. These
conditions represent

__________________
variables.
An experiment is designed to isolate the factor you are interested in testing, the
____________________ variable. All other conditions are held constant
to insure that your observed results were caused by the only factor that was varied.
SCIENTIFIC METHOD
Page 1-6
__________________.

Name the dependent variable in this experiment:

You decide to measure the growth of your plants (height in centimeters) once a week for
a month. You will keep detailed records of your observations.

It is helpful to develop an experiment using a group of plants (or animals), instead of just
one. There are two good reasons for this:
1. If unexpected factors, such as disease, affect one or two experimental subjects, it will
not ruin the entire experiment.
2. Natural genetic variability will cause some plants to grow taller than others, just as
some people grow taller than others. You can minimize this effect by measuring
height in a group of plants.

You decide that 10 plants will receive identical measured amounts of fertilizer each
__________________
week. These are considered the
group of plants.
They are receiving the treatment that will help you test your original hypothesis.

Ten plants will receive no fertilizer. These are the _____________________________
group of plants. They are used as a comparison to the first group in order to interpret
your results, hopefully showing any observed differences in height in the two groups are
due to the only difference between them, the application of fertilizer.
Based on this experimental plan, answer the following questions IN COMPLETE
SENTENCES.
1. Why is it necessary to divide the plants into two groups?
2. Why is it important to maintain identical conditions in both groups EXCEPT for the
application of fertilizer?
3. Why is it better to use ten plants in each group instead of just one or two? Give TWO
reasons and use YOUR OWN WORDS.
a.
b.
SCIENTIFIC METHOD
Page 1-7
LAB EXERCISE TWO (Pages 7-15 )
Collecting and Organizing Data
The month has ended and you are now ready to draw conclusions from your data. You will be
thinking about what your results mean and whether your hypothesis is supported. The
information you collected during your experiment is recorded in Table 1-1. Calculate total
height gain for each plant, all plants and the average height gain for the experimental and control
groups.
Table 1-1A
HEIGHT GAIN OVER FOUR WEEKS
Initial
Height,
Plant No.
cm
Week 1
WITHOUT FERTILIZER:
1
10.0
1.6
Total
Height
Gain, cm
Average
Height
Gain, cm
Week 2
Week 3
Week 4
2.0
3.0
2.5
---
2
11.5
2.2
1.5
1.5
2.0
---
3
9.6
1.5
2.3
2.6
2.0
---
4
9.2
2.0
3.0
2.8
1.5
---
5
10.2
2.3
1.2
1.6
2.0
---
6
11.0
3.2
1.7
2.0
3.2
---
7
10.0
2.6
3.0
3.0
1.4
---
8
9.7
4.0
2.6
4.0
2.3
---
9
10.4
DIED
---
---
---
---
10
10.4
2.3
2.3
2.7
2.0
---
TOTALS
SCIENTIFIC METHOD
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Table 1-1B
HEIGHT GAIN OVER FOUR WEEKS
Initial
Height,
Plant No.
cm
Week 1
WITH FERTILIZER:
1
9.6
4.2
Total
Height
Gain, cm
Average
Height
Gain, cm
Week 2
Week 3
Week 4
5.0
3.0
4.7
---
2
9.8
6.0
4.0
5.5
5.0
---
3
10.3
5.3
5.5
3.6
4.2
---
4
11.0
2.1
3.2
6.2
3.8
---
5
10.1
3.4
4.0
4.4
4.0
---
6
9.2
4.7
3.1
3.1
4.0
---
7
9.5
4.2
5.2
3.9
3.6
---
8
10.0
3.3
6.0
5.6
4.2
---
9
9.7
5.8
6.1
6.5
5.0
---
10
10.4
5.1
3.4
5.8
5.3
---
TOTALS
Based on Table 1-1A and B, answer the following questions using complete sentences.
4. Were there noticeable growth differences between the plants given fertilizer versus those that
were not? If so, which group grew taller? Cite evidence from your table to support your
answer.
5. Do these results support the original hypothesis? Explain your answer.
6. Why is it more accurate to compare the average height increases of the control and
experimental groups, instead of comparing individual plants?
7. Calculate the final height of control plant number three. Show your work.
8. Finally, answer the following questions that relate to the following scientific situation:
A group of students is studying the effect of temperature on bacterial growth. The bacteria
are collected on Petri dishes containing nutrient agar. They are placed in an incubator
(37oC), the lab room (21oC), a refrigerator (10oC) and a freezer (0oC). Bacterial growth is
measured by estimating the percentage of each dish covered by bacteria at the end of a threeday growth period.
a. Identify a possible hypothesis the scientists are testing?
b. What is the independent variable?
c. What is the dependent variable?
d. What variables should remain constant (list at least two)?
SCIENTIFIC METHOD
Page 1-9
In addition to applying a particular method of approaching and solving problem, the scientific
method, scientists also use standard methods to collect and present data. The results of an
experiment must be presented in a clear and concise format. In this lab you will learn to present
and interpret scientific data.
Tables
Tables are used to record collected data. From this point, data can be modified or rearranged to
suit the needs of the experiment. For instance, a team of students performed an experiment to
identify any differences between the resting pulse rates and after-exercise pulse rates for athletes
and nonathletes. The experiment was conducted using the same controlled variables (time, type
of exercise, etc.). They recorded their data in table format with a descriptive title and column
headings. This data is presented in Table 1-2.
Table 1-2
DATA COLLECTION - PULSE RATE OF NONATHLETES VS. ATHLETES
Nonathletes
Athletes
Resting Pulse
After Exercise
Resting Pulse
After Exercise
Trial
Trial
Trial
Trial
Subj
1
2
3
1
2
3
Subj
1
2
3
1
2
3
1
72
68
71
145 152 139
1
67
71
70
136 133 134
2
65
63
72
142 144 158
2
73
71
70
141 144 142
3
63
68
70
140 147 144
3
72
74
73
152 146 149
4
70
72
72
133 134 145
4
75
70
72
156 151 151
5
75
76
77
149 152 153
5
78
72
76
156 150 155
6
75
75
71
154 148 147
6
74
75
75
149 146 146
7
71
68
73
142 145 150
7
68
69
68
132 140 136
8
68
70
66
135 137 135
8
70
71
70
151 148 146
9
78
75
80
160 155 153
9
73
77
76
138 152 147
10
73
75
74
142 146 140
10
72
68
64
153 155 155
To the casual reader, this data is meaningless. It is simply a list of numbers. In this form, it is
called raw data and shows the data collected by the team without any kind of summarization.
Each subject repeated the experiment in three trials under identical conditions to see if the results
were consistent. An identical answer for each subject’s trial is not expected because a certain
amount of variation is expected in biological systems. By replicating the experiment, scientists
are able to normalize the amount of variation in the system by calculating an average from the
different trials. Complete this work for nonathletes and athletes in Table 1-3 on the next page.
SCIENTIFIC METHOD
Page 1-10
Table 1-3
SUBJECT’S AVERAGE PULSE RATE AND OVERALL AVERAGES
(average of 3 trials / subject; pulse taken after 5-min step test and again following 5 min rest)
Subject
Nonathletes
Resting Pulse
After
Average,
Exercise
beats/min
Average,
beats/min
Athletes
Resting Pulse
After
Average,
Exercise
beats/min
Average,
beats/min
1
2
3
4
5
6
7
8
9
10
Overall
Averages
Notice the title describes the table’s contents and includes a subtitle to identify the experimental
conditions and number of replications used to calculate the averages. The units of the dependent
variable (pulse rate) are ALWAYS given for both nonathletes and athletes (independent variable)
under both conditions in the headings.
In order to minimize confusion for the reader, tables should present results that have relatively
few data points. Tables are also useful to display several dependent variables at the same time.
For example, if blood pressure before and after exercise and recovery time were measured in this
experiment, these results could be summarized in one table.
Graphs
Numerical results of an experiment are often presented in a graph rather than a table. A graph is
literally a picture of the results and can be more easily interpreted than a table. Generally, the
independent variable is graphed on the x-axis (horizontal) and the dependent variable is graphed
the y-axis (vertical). By looking at a graph, the effect the independent variable has on the
dependent variable can be determined. A review of the different types of variables may be
helpful; refer to the lab that explains the scientific method.
SCIENTIFIC METHOD
Page 1-11
When you are drawing a graph or making a graph on the computer, keep in mind that your
objective is to show the data in the clearest, most readable form possible. In order to achieve
this, observe the following rules:

Use graph paper to plot the values correctly.

Plot the independent variable on the x-axis and the dependent variable on the y-axis.
EXAMPLE: if you are graphing the effect of the amount of fertilizer on peanut weight, the amount of
fertilizer is plotted on the x-axis and peanut weight is plotted on the y-axis. Refer to Figure 1-1

Label each axis with the name of the variable and specify the units used to measure it
EXAMPLE: x-axis is labeled “Fertilizer Applied (g/100 m2)”; y-axis is labeled: “Weight of Peanuts per
Plant (grams)”. Refer to Figure 1-1

The intervals labeled on each axis should be appropriate for the range of data so that most of
the area of the graph can be used.
EXAMPLE: if values range from 0 to 50, you label the entire length of the axis at 0, 10, 20, etc. It would
be confusing to have labels that correspond to the actual data points (i.e., 2, 17, 24, 42, 47). Refer to
Figure 1-1
A graph should have a title that describes the experimental conditions that produced the
data. Refer to Figure 1-1

Use a legend when there is more than one set of data points plotted.
Figure 1-1
WEIGHT OF PEANUTS PRODUCED VARYING FERTILIZER CONCENTRATION
(average seed weight per plant in 100 m2 plots, 400 plants/plot)
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The most commonly used graphs are line graphs and bar graphs. In a line graph, data are
plotted as separate points on the axes, and the points are connected to each other. To show a
trend, draw smooth curves. They are used to illustrate variables that have an unlimited number
of values between points; for example, growth of a plant over a specific time frame. Bar graphs
are used when the variable has a limited number of possible values with no values in between
them. Another way to say it is that Bar graphs represent separate or discrete groups or categories,
thus emphasizing the differences between the group; for example, the type of fertilizer used in an
experiment. When there is more than one set of data on a graph, it is necessary to provide a key
or legend which indicates which line corresponds to which data set whether you are using a bar
or line graph.
Based on this information, construct a graph (make a pencil graph or insert a computer graph)
that illustrates the overall averages generated in Table 1-3 on page 11. What type of graph are
you going to use? And why?
_________________________________________________
_________________________________________________
Be sure to follow the rules outlined above for developing an accurate graph.
Figure 1-2
____________________________________________
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Can the information on your graph in Figure 2-2 be presented another way? If so, describe how?
Data Interpretation
Once you understand how tables and graphs are constructed, it is easier to obtain information
from the graphs you may encounter in the future. For the graphs below, write a sentence or two
to answer the question describing what each graph illustrates.
Figure 1-3
CHANGE IN WORLD POPULATION FROM 1600 TO 2000
World Population (millions)
10000
8000
6000
4000
2000
0
1600
1650
1700
1750
1800
1850
1900
1950
2000
2050
Year
Use Figure 1-3 to answer the next THREE questions USING COMPLETE SENTENCES.
1. What does this graph show? Be very specific.
2. What was the world’s population in 1900?
3. Predict the world’s population in 2050 based on the plotted line, assuming the current trend
continues.
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There may be occasions where instead of connecting the points of a line graph, you will be asked
to draw a “best fit” line between them. This line may or may not pass through any of these
points but represents the trend of this data. Typically, this line begins through the origin (0,0).
Figure 1-4
AMOUNT OF GLUCOSE DETECTED IN BLOODSTREAM
2.00
y = 0.0527x
Glucose, ug/mL
1.50
1.00
0.50
0.00
0
5
10
15
20
25
30
35
Time, min
From this line, the amount of glucose can be estimated or calculated for any value of time that
falls within this range. To estimate the amount of glucose after 23 minutes, draw a line up from
the x-axis at 23 and then across to the concentration of glucose. To calculate the amount of
glucose after 23 minutes, use the equation of the “best fit” line.
Est’d Concentration, ug/mL:
_______
Which value is more accurate? Why?
Calc’d Concentration, ug/mL:
_______
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Page 1-15
Figure 1-5
POPULATION GROWTH OF Paramecium aurelia AND Paramecium caudatum WHEN
GROWN SEPARATELY AND TOGETHER
Population Density
1000
Grown Separately
800
600
400
P. aurelia
P. caudatum
200
0
0
2
4
6
8
10
12
14
16
18
Days
Population Density
1000
Grown Together
800
600
P. aurelia
400
P. caudatum
200
0
0
2
4
6
8
10
Days
12
14
16
18
Use Figures 1-5 to answer the next THREE questions USING COMPLETE SENTENCES.
4. Describe what this graph shows. Be thorough and discuss the similarities and differences
between these two graphs.
5. On what day does Paramecium aurelia reach its maximum population density? Does this
apply in both graphs?
6. Does Paramecium caudatum do better when it is grown alone or when it is grown in the
presence of Paramecium aurelia? Hypothesize on why this might occur.
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LAB EXERCISE THREE (Page 16, Two graphs and explanations in your notebook)
List of Environmental Agencies and Organizations
http://www.epa.gov/
http://www.epa.gov/epahome/scidata.htm
http://www.agr.state.nc.us/
http://www.enr.state.nc.us/
http://www.ncdmf.net/index.html
http://www.esb.enr.state.nc.us/Fishkill/fishkillmain.htm
http://www.p2pays.org/ref/02/01622/index.htm
http://www.ncwildlife.org/fs_index_10_kids.htm
http://www.dhhs.state.nc.us/
http://www.ncwildlife.org/
http://www.usdoj.gov/enrd/
http://www.nps.gov/
http://www.whitehouse.gov/ceq/
Now go to at least two different sites listed above. Find two different graphs, copy them into a
word document and then in a paragraph explain the results of each graph. Be sure to site the
website where you retrieved the graph. Your graphs should be in your notebook, when it is
turned in.