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Principles of Biology
3
contents
Practicing Biology
Biological scientists use a process of inquiry that has developed over centuries and
involves the collaboration of a global community.
Biologists study the natural world in a variety of ways.
Biologists conduct scientific research both in the lab and in the field.
(left) Scott Bauer/Courtesy of U.S. Department of Agriculture. (right) Courtesy of Neal Snyder/U.S. Army
Environmental Command.
Topics Covered in this Module
The Scientific Method
Scientific Communication
Major Objectives of this Module
Describe the scientific method.
Describe how data are analyzed.
Describe different types of experimental setups.
page 14 of 989
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Principles of Biology
3 Practicing Biology
Charles Darwin visited the Galápagos Islands in 1835 and collected finch
specimens. He observed that the size and shape of the finches' beaks varied
widely among species, depending on diet: seed eaters tended to have wide,
strong beaks, while insect eaters tended to have narrow long beaks. Yet
similarities existed among the birds as well. From these observations, Darwin
concluded that at one time only one species of finch existed on the islands.
Darwin speculated that individuals with a competitive advantage for a given
ecological niche were better able to survive and reproduce than other
members of a population, and over many generations, the population
evolved into different species. He called this mechanism of evolution natural
selection. More recently, scientists have compared the DNA sequence of
various finch species from the Galápagos Islands and found similarities
indicating that the birds do have a common ancestor.
Both Darwin and these modern scientists are biologists, or scientists who
study life. Biologists, like all scientists, use a process called the scientific
method to advance their understanding of the natural world.
The Scientific Method
Science is a way of learning about the universe through a formal process of
observation and experimentation called the scientific method. Although
humans have made informal observations and experimentations since
antiquity, the scientific method developed gradually. The process of
observation was formalized by the Greek philosopher Aristotle (384–322
BCE; Figure 1). Aristotle framed questions based on observations and
answered these questions to learn "truths" about the universe. This type of
analysis, in which general conclusions are drawn from specific observations,
is called inductive reasoning. Inductive reasoning is an important part of
the scientific method, but Aristotle believed that only observation, not
experimentation, could be used to learn the truth. Three Arabic scientists are
primarily credited with the development of experimental science: Jābir ibn
Hayyān (721–815), Abū Rayḥān al-Bīrūnī (973–1048), and ibn Sīnā (also
known as Avicenna, 980-1037). Experimental science involves a different
type of reasoning, called deductive reasoning. In deductive reasoning,
specific results are predicted from a general premise.
contents
Figure 1: Aristotle, painted centuries
after his death by Francesco Hayez.
The Greek philosopher Aristotle is
credited with the development of formal
inductive reasoning.
Francesco Haez, Aristotle, 1811.
In modern practice, an observation may involve simply watching (for
example, a scientist may watch a bird feeding its young), or it may involve
careful measurements (the scientists may weigh the chicks). Measurements
and visual observations that are recorded are called data (singular, datum).
From observations, scientists form a hypothesis, a tentative answer to a
well-framed question. A hypothesis must be framed so that it is falsifiable,
meaning that it can be proven wrong through experimentation. For example,
a scientist might observe that some chicks are more brightly colored than
others. This may lead the scientists to wonder, "What competitive advantage
does the bright color confer?" A tentative answer to this question may be
"The parents preferentially feed brightly colored chicks." It is important to
emphasize that this is a tentative answer, or hypothesis. To test this
hypothesis, the scientist would need to conduct a carefully controlled test
called an experiment. Notice that in this example, inductive reasoning
(bright color must confer some competitive advantage) leads to deductive
reasoning (the parents preferentially feed brightly colored chicks). Cycles of
inductive and deductive reasoning are central to the scientific method.
Figure 2: Scientific reasoning.
Two types of reasoning occur in
science: inductive reasoning and
deductive reasoning.
© 2014 Nature Education All rights
reserved.
The example experiment discussed here is one that has in fact taken place.
A species of bird called coots has brightly colored chicks, and scientists
hypothesized that parents might preferentially feed chicks with brighter
plumage. To test their hypothesis, they measured three parameters: feeding
rate, growth rate (assessed by measuring the length of chicks), and survival
rate. From their hypothesis that the parents preferentially feed the brightly
colored chicks, the scientists predicted that the feeding rate, growth rate, and
survival rate would all be higher for brightly colored chicks. To conduct the
experiment, scientists clipped the bright feathers from half of the chicks in a
brood and left the bright feathers of the other half untouched. Feeding,
growth, and survival rates were all higher for the brightly colored chicks.
These results support the hypothesis that parents preferentially feed brightly
colored offspring. However, a hypothesis can never be proven because there
always might be an alternative explanation for positive results. For example,
it is possible that the parents were able to discern that the dull chicks had
been handled, and this handling, rather than feather color, resulted in
differential treatment. For this reason, many experiments and observations
are needed to advance scientific knowledge. Many students believe that a
good hypothesis is one that is correct, but in reality, any hypothesis that is
testable is a good hypothesis, even if it is ultimately proven wrong. In fact,
many of the greatest advances in science occur when a hypothesis is proven
wrong: when this happens, scientists are forced to question their reasoning
and may come to a completely different, better understanding of natural
phenomena.
Analyzing data.
In the hypothetical experiment shown in Figure 3, reaction time of eight test
subjects is measured when they are talking on a cell phone and when they
are not. This experiment generates two groups of data: an experimental
group that receives treatment (or in this case uses cell phones) and a
control group that does not. Notice that the terms experimental and control refer
to the data points, not the individuals being tested. In this particular
experiment, each test subject appears in both groups, although this is not
always the case. An experiment in which one group receives treatment and
the other does not is called a controlled experiment.
Figure 3: Setup and results for a hypothetical scientific experiment.
(1) Researchers observe that more accidents occur when a driver is using
a cell phone; using inductive reasoning, the researchers hypothesize that
cell phone use increases reaction time. (2) To measure reaction time
experimentally, subjects are asked to loosely grasp a ruler at the zero
mark and to grab it when the experimenter drops it. Reaction time is
measured when test subjects are using a cell phone (experimental group)
and when they are not (control group). (3) The researchers conducting the
experiment record the number at which the ruler is grabbed and calculate
the mean and standard deviation. (4) Reaction time is slower when a cell
phone is being used. The data support the hypothesis that cell phone use
increases reaction time.
© 2014 Nature Education All rights reserved.
In a controlled experiment, the variable that differs between the experimental
and control groups, or the one that is controlled by the scientist, is called the
independent variable. Data collected in an experiment are called
dependent variables because they depend on the independent variable. In
the cell phone experiment, reaction time (the dependent variable) depends
on cell phone usage (the independent variable).
Look carefully at data points in Figure 3, panel 3: they vary widely, and
although reaction time is usually faster for the control group, in one case it is
not. Because variability occurs in scientific measurements, measurements
must be repeated, and a mathematical analysis must be used to determine
whether data is statistically significant. Statistical significance refers to the
probability that a given result is not due to random chance.
The mean, or average, is a common statistical test that is calculated by
adding all the values in a data set and dividing by the number of data points
(N). The symbol Σ means "the sum of," so mean can be calculated using the
following equation:
Mean = Σ/N
The mean reaction time for the experimental group (4.4) is slower than the
mean reaction time for the control group (2.3). Another statistical value that
is commonly calculated is the variance. Variance, a measure of how much
spread there is in the data, is calculated using the following equation:
© 2014 Nature Education All rights reserved.
From the variance, the standard deviation can be calculated. The standard
deviation is a measure of dispersion from the mean. The lower the standard
deviation, the less the dispersion. Standard deviation is the square root of
the variance:
© 2014 Nature Education All rights
reserved.
Standard deviation is often written in the following format: mean ± standard
deviation. Thus, the data for the experimental group is written as follows: 4.4
± 1.5; and the data for the control group is written as follows: 2.3 ± 1.0.
Experimental setups.
Unintentional bias of both scientists and human test subjects can potentially
skew results. For example, an experimental subject receiving an
investigational drug may feel better simply because he thinks the drug is
effective. Likewise, the researcher conducting the drug trial may rate
improvement of experimental subjects as better than control subjects. For
this reason, most clinical studies are double blind, meaning that neither the
researcher nor the test subjects know who is in the experimental group and
who is in the control group. In clinical drug trials, subjects in the control group
are given a placebo (a drug that looks the same as the real drug but contains
no active ingredients) and otherwise treated exactly the same as the test
subjects to ensure that the results are not skewed by unintentional bias or
differences in treatment.
Although controlled experiments are the ones that students are generally
most familiar with, researchers devise other types of experiments when it is
impossible, impractical, or unethical to set up a controlled experiment.
Examples of other experimental setup include natural experiments,
regression analysis, and active controlled experiments. In a natural
experiment, two existing natural populations, such as smokers and
non-smokers, are compared. In a regression analysis experiment, varying
levels of treatment are applied to test subjects. For example, varying levels
of an experimental drug may be given to different patients to optimize
dosage and minimize side effects. In an active controlled experiment, the
experimental group is given a new treatment, and the control group is given
an existing treatment. Active controlled experiments are used to test new
antibiotics: in such experiments, all patients receive an antibiotic to treat an
infection, but some receive a new one, while others receive a standard
treatment. Regardless of what experimental setup is used, the population of
the experimental and control groups should be similar in regard to age, sex,
health, and other variables.
Scientific laws and theories.
A scientific law is a general statement based on repeated observations that
can be used to predict future observations. In biology, the statement that "the
cell is the basic unit for all forms of life" is a scientific law based on many
years of research by many scientists. Because the concept that all life is
cell-based is scientific law, scientists can predict that organisms found in the
future will be cell-based. A scientific theory attempts to explain a broad
group of laws and observations. The concept that natural selection results in
evolution is a theory that attempts to explain how differences arose among
various organisms that appear to have a common ancestor.
Test Yourself
How does a hypothesis differ from a scientific law?
Submit
IN THIS MODULE
The Scientific Method
Scientific Communication
Summary
Test Your Knowledge
WHY DOES THIS TOPIC MATTER?
A Sea of Microbes Drives Global
Change
Do floating microbes in the ocean’s
surface waters play an outsize role in global
climate?
Stem Cells
Stem cells are powerful tools in
biology and medicine. What can
scientists do with these cells and their
incredible potential?
Cancer: What's Old Is New Again
Is cancer ancient, or is it largely a
product of modern times? Can
cutting-edge research lead to prevention
and treatment strategies that could make
cancer obsolete?
The Climate Connection
How is life on Earth reacting to
climate change?
PRIMARY LITERATURE
Brain preplay anticipates the
future
Preplay of future place cell sequences by
hippocampal cellular assemblies.
View | Download
Classic paper: The discovery of
the neutron (1932)
Possible existence of a neutron.
View | Download
Aneuploids may not be so
abnormal
Aneuploidy confers quantitative proteome
changes and phenotypic variation in budding
yeast.
View | Download
A new technique for detecting
autoimmune diseases
Autoantigen discovery with a synthetic
human peptidome.
View | Download
page 15 of 989
3 pages left in this module
Principles of Biology
contents
3 Practicing Biology
Scientific Communication
The seventeenth-century physicist Sir Isaac Newton said, "If I have seen
further, it is by standing on the shoulders of giants," meaning that an
understanding of the works of his predecessors was critical to his success.
Today, as in Newton's time, scientific advancement requires a broad
scientific knowledge.
The best source for quality scientific research is peer-reviewed journals. All
the research published in these journals must pass a peer-review process, in
which anonymous scientists decide whether the research merits publication
and whether further experiments are necessary. Other important sources of
information include review articles written by well-established scientists and
databases containing collections of scientific data from various sources.
Although the format of different journals varies considerably, a peer-reviewed
scientific paper will generally include the following sections:
(1) Abstract. The abstract is a short, one- or two-paragraph summary of the
hypothesis being tested, the methods, results, and conclusion.
(2) Introduction. The introduction provides the context for the work being done.
It usually begins with a broad overview and then focuses on the specific
research being conducted.
(3) Materials and Methods. The materials and methods section provides a
summary of reagents and equipment used as well as a specific explanation
of how the experiments were conducted. Usually the Materials and Methods
section follows the introduction, but sometimes it is placed at the end.
(4) Results. The results section includes all of the data collected. Often, tables
and graphs are included to show the data visually.
(5) Discussion. The discussion states whether or not the results support the
hypothesis. The discussion may also describe concerns with the current
study and give suggestions for future studies.
(6) References. This final section of the paper lists the research articles and
other sources of information cited in the paper.
IN THIS MODULE
The Scientific Method
Scientific Communication
Summary
Test Your Knowledge
WHY DOES THIS TOPIC MATTER?
A Sea of Microbes Drives Global
Change
Do floating microbes in the ocean’s
surface waters play an outsize role in global
climate?
Stem Cells
Stem cells are powerful tools in
biology and medicine. What can
scientists do with these cells and their
incredible potential?
Cancer: What's Old Is New Again
Is cancer ancient, or is it largely a
product of modern times? Can
cutting-edge research lead to prevention
and treatment strategies that could make
cancer obsolete?
How is life on Earth reacting to climate
The Climate Connection
change?
PRIMARY LITERATURE
Brain preplay anticipates the
future
Preplay of future place cell sequences by
hippocampal cellular assemblies.
View | Download
Classic paper: The discovery of
the neutron (1932)
Possible existence of a neutron.
View | Download
Aneuploids may not be so
abnormal
Aneuploidy confers quantitative proteome
changes and phenotypic variation in budding
yeast.
View | Download
A new technique for detecting
autoimmune diseases
Autoantigen discovery with a synthetic
human peptidome.
View | Download
page 16 of 989
2 pages left in this module
Principles of Biology
3 Practicing Biology
Summary
Describe the scientific method.
The scientific method is a process of learning about the world through
observation and experimentation. Two types of reasoning are used in the
course of scientific research: inductive reasoning and deductive reasoning. In
inductive reasoning, a general conclusion is drawn from specific
observations. In deductive reasoning, specific results are predicted from a
general premise.
OBJECTIVE
A hypothesis is formed through inductive reasoning and is a tentative answer
to a well-framed question. A scientific law is a general statement
summarizing many observations. Laws are based on many experiments that
all support the same hypothesis. A scientific theory is an explanation for laws
and hypotheses.
Describe how data are analyzed.
In a controlled experiment, an experimental group, which receives treatment,
is compared to a control group, which does not receive treatment. The
variable that differs between the experimental and control groups is called
the independent variable, and the data collected in an experiment are
called dependent variables. In any experiment, data must be
mathematically analyzed to determine whether it is statistically significant.
OBJECTIVE
Describe different types of experimental setups.
In a controlled experiment, the experimental group receives the treatment
and the control group does not. In a natural experiment, two different natural
populations are compared. In a regression analysis experiment, varying
levels of treatment are compared. In an active controlled experiment, a new
treatment is compared to an old one.
OBJECTIVE
Key Terms
active controlled experiment
Experiment in which one group is given a new treatment, and another group is
given an existing treatment.
control group
A group that does not receive treatment in an experiment.
controlled experiment
An experiment in which one group receives treatment and the other does not.
data (singular datum)
Recorded observations or measurements.
deductive reasoning
Predicting a specific result from general principles.
dependent variable
Measured results of an experiment; dependent on the independent variable.
double blind
Experiment in which neither researcher nor subject knows who is in the treatment
group or the control group until after the data have been collected.
experiment
A carefully controlled observation.
experimental group
A group that receives treatment in an experiment.
contents
hypothesis
Tentative answer to a well-framed question.
independent variable
The variable that is controlled by the scientist.
inductive reasoning
Inferring general principles from specific observations.
law
A general statement, based on repeated observations, that can be used to predict
future observations.
mean
The average, calculated by adding together individual values and dividing by the
number of values in the set.
natural experiment
An experiment in which two existing natural populations are compared.
natural selection
A process through which advantageous traits are passed from one generation to
the next because individuals with those traits are better able to survive and
reproduce.
observation
A description or measurement of a natural phenomenon.
regression analysis experiment
An experiment in which varying levels of treatment are applied to test subjects.
science
A systematic enterprise that builds and organizes knowledge in the form of
testable explanations and predictions about the universe.
scientific inquiry
Search for information and explanation.
scientific method
A process of learning through observation and experimentation.
standard deviation
A measure of deviation from the mean.
statistical significance
Probability that a given result is not due to random chance.
theory
An explanation for observations.
variance
A measure of the spread in data.
IN THIS MODULE
The Scientific Method
Scientific Communication
Summary
Test Your Knowledge
WHY DOES THIS TOPIC MATTER?
A Sea of Microbes Drives Global
Change
Do floating microbes in the ocean’s
surface waters play an outsize role in global
climate?
Stem Cells
Stem cells are powerful tools in
biology and medicine. What can
scientists do with these cells and their
incredible potential?
Cancer: What's Old Is New Again
Is cancer ancient, or is it largely a
product of modern times? Can
cutting-edge research lead to prevention
and treatment strategies that could make
cancer obsolete?
The Climate Connection
How is life on Earth reacting to
climate change?
PRIMARY LITERATURE
Brain preplay anticipates the
future
Preplay of future place cell sequences by
hippocampal cellular assemblies.
View | Download
Classic paper: The discovery of
the neutron (1932)
Possible existence of a neutron.
View | Download
Aneuploids may not be so
abnormal
Aneuploidy confers quantitative proteome
changes and phenotypic variation in budding
yeast.
View | Download
A new technique for detecting
autoimmune diseases
Autoantigen discovery with a synthetic
human peptidome.
View | Download
page 17 of 989
1 pages left in this module
Principles of Biology
contents
3 Practicing Biology
Test Your Knowledge
1. Which term describes the data that are collected during an experiment?
independent variable
dependent variable
control group
hypothesis
conclusion
2. Which of these is a characteristic of a good hypothesis?
It is based on previous observations or results.
It cannot be tested.
It cannot be falsified.
It is correct.
None of these choices is correct.
3. How might a scientific theory be modified?
by a change in the experimental methods that leads to the same result
by the declaration of a scientific society
Theories cannot be changed. They are natural laws.
by consensus of the top scientists in the field
by the uncovering of new information
4. Students compared their resting heart rate to their heart rate after exercise. They
measured their resting heart rate after sitting for five minutes; they then did 50
jumping jacks and afterward measured their heart rate. What was the dependent
variable of this study?
whether or not the person was resting when the heart rate was measured
how many jumping jacks were done
heart rate
how long the person rested before heart rate was measured
There was no dependent variable.
5. Which of the following statements about types of experimental setup is correct?
A controlled experiment is one in which the experimental group receives the
treatment and the control group does not.
A natural experiment is one in which two different natural populations are
compared.
A regression analysis experiment is one in which varying levels of treatment are
compared.
An active controlled experiment is one in which a new treatment is compared to an
old one.
All of the answers are correct.
Submit
IN THIS MODULE
The Scientific Method
Scientific Communication
Summary
Test Your Knowledge
WHY DOES THIS TOPIC MATTER?
A Sea of Microbes Drives Global
Change
Do floating microbes in the ocean’s
surface waters play an outsize role in global
climate?
Stem Cells
Stem cells are powerful tools in
biology and medicine. What can
scientists do with these cells and their
incredible potential?
Cancer: What's Old Is New Again
Is cancer ancient, or is it largely a
product of modern times? Can
cutting-edge research lead to prevention
and treatment strategies that could make
cancer obsolete?
The Climate Connection
How is life on Earth reacting to
climate change?
PRIMARY LITERATURE
Brain preplay anticipates the
future
Preplay of future place cell sequences by
hippocampal cellular assemblies.
View | Download
Classic paper: The discovery of
the neutron (1932)
Possible existence of a neutron.
View | Download
Aneuploids may not be so
abnormal
Aneuploidy confers quantitative proteome
changes and phenotypic variation in budding
yeast.
View | Download
A new technique for detecting
autoimmune diseases
Autoantigen discovery with a synthetic
human peptidome.
View | Download
page 18 of 989