1-1 What Is Science?
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What Science Is and Is Not
What Science Is and Is Not
What is the goal of science?
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What Science Is and Is Not
The goal of science is to:
• investigate and understand the natural world.
• explain events in the natural world.
• use those explanations to make useful predictions.
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What Science Is and Is Not
Science is an organized way of using evidence to
learn about the natural world.
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Thinking Like a Scientist
Thinking Like a Scientist
Scientific thinking begins with observation.
Observation is the process of gathering information about
events or processes in a careful, orderly way.
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Thinking Like a Scientist
The information gathered from observations is
called data.
• Quantitative data
• Qualitative data
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Thinking Like a Scientist
Scientists use data to make inferences.
An inference is a logical interpretation based on
prior knowledge or experience.
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Explaining and Interpreting Evidence
Explaining and Interpreting Evidence
A hypothesis is a proposed scientific explanation for a set
of observations.
A hypothesis may be ruled out or confirmed.
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Explaining and Interpreting Evidence
Hypotheses are tested by performing controlled
experiments or by gathering new data.
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Explaining and Interpreting Evidence
Researchers often work in teams to analyze,
review, and critique each other’s data and
hypotheses.
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Science as a Way of Knowing
Science as a Way of Knowing
Science is an ongoing process that involves:
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asking questions
observing
making inferences
testing hypotheses
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How a Theory Develops
How does a scientific theory develop?
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How a Theory Develops
How a Theory Develops
As evidence from numerous investigations builds
up, a hypothesis may become so well supported
that scientists consider it a theory.
In science, the word theory applies to a well-tested
explanation that unifies a broad range of
observations.
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Major Theories in Biology
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Germ Theory
Evolutionary Theory
Cell Theory
Gene Theory
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Science as a Way of Knowing
Scientific understanding is always changing.
Good scientists are skeptics who question both
existing ideas and new hypotheses.
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Science and Human Values
Science and Human Values
An understanding of science and the scientific approach is
essential to making intelligent decisions.
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Science and Human Values
Decisions involve many factors besides
scientific information, including:
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the society in which we live
economic considerations
laws
moral principles
Citizens decide what to do when they vote.
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Pseudo science looks like science but it is
•Not testable/falsifiable/refutable
•Relies on anecdotes, not experimental data
•Does not change in face of new evidence
• Uri Geller
• Magic water
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1–1
Observations involving numbers are known as
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qualitative observations.
hypothetical observations.
quantitative observations.
inferred observations.
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1–1
Which of the following shows the interaction of
science and human values?
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the debate over the best way to produce electricity
investigating how a manatee behaves
Determining what causes a disease
using a hypothesis to test an explanation
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1–1
A scientist takes paint chips from 10 apartments in a
large building. She tests for the presence of lead in
the paint and finds it in all 10 samples. She then
concludes that lead paint is probably present in all
120 apartments in the building. This conclusion is
an example of
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a scientific fact.
a scientific error.
proof.
a reasonable inference.
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1–1
A possible explanation for a set of observations is
known as
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data.
a hypothesis.
an inference.
a result.
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1–1
A good scientific hypothesis must be
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correct.
able to be tested.
obvious.
based on common sense.
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Designing an Experiment
How do scientists test hypotheses?
A hypothesis should be tested by an experiment in
which only one variable is changed at a time.
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Designing an Experiment
Designing an Experiment
The process of testing a hypothesis includes:
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Asking a question
Forming a hypothesis
Setting up a controlled experiment
Recording and analyzing results
Drawing a conclusion
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Designing an Experiment
Setting Up a Controlled Experiment
Manipulated/Independent variable
Responding/Dependent variable
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• When graphing, always title graph
“Dependent variable” as a function of
“Independent variable”
• If a scientist wants to examine how light levels
affect tree growth, which is the dependent
variable? Which is the independent variable?
• Which is X? Which is Y?
• Y as a function of X
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Designing an Experiment
Asking a Question
Many years ago, people wanted to know how living
things came into existence. They asked:
How do organisms come into being?
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Designing an Experiment
Forming a Hypothesis
One early hypothesis was spontaneous generation.
For example, most people thought that maggots
spontaneously appeared on meat.
In 1668, Redi proposed a different hypothesis: that
maggots came from eggs that flies laid on meat.
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Designing an Experiment
Redi’s Experiment
Uncovered jars
Controlled Variables:
jars, type of meat,
Location, temperature,
time
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Covered jars
Designing an Experiment
Redi’s Experiment
Manipulated Variable:
Gauze covering that keeps
flies away from meat
Responding Variable:
whether maggots appear
Several
days pass.
Maggots appear.
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No maggots appear.
Designing an Experiment
Drawing a Conclusion
Scientists use the data from an experiment to evaluate a
hypothesis and draw a valid conclusion.
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Repeating Investigations
Spallanzani's Test of Redi's Findings
Gravy is boiled.
Gravy is boiled.
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Repeating Investigations
Spallanzani's Test of Redi's Findings
Flask is sealed.
Flask is open.
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Repeating Investigations
Spallanzani's Test of Redi's Findings
Gravy is teeming
with microorganisms.
Gravy is free of
microorganisms.
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Repeating Investigations
Pasteur's Test of Spontaneous Generation
– Louis Pasteur conclusively disproved the hypothesis of
spontaneous generation.
– Pasteur showed that all living things come from other living
things.
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Repeating Investigations
Pasteur’s Experiment
Broth is boiled
Broth is free
of microorganisms
for a year.
Curved neck is
removed.
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Broth is
teeming with
microorganisms.
Repeating Investigations
The Impact of Pasteur’s Work
Pasteur saved the French wine industry, which was troubled
by unexplained souring of wine.
He began to uncover the nature of infectious diseases,
showing that they were the result of microorganisms.
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1–2
In an experiment, the variable that is deliberately
changed is called the
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control.
manipulated variable.
responding variable.
constant control
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1–2
The mistaken belief that living organisms can arise
from nonliving matter is called
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biogenesis.
Pasteur's theory.
spontaneous generation.
Spallanzani’s hypothesis.
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1–2
Which of the following was the manipulated
variable in Redi’s experiment?
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the kind of meat used
the temperature the jars were kept at
the gauze covering on some jars
the kind of fly that visited the jars
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1–2
A well-tested explanation that unifies a broad
range of observations is a
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hypothesis.
variable.
control.
theory.
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1–2
A scientific explanation does not become a theory
until
• a majority of scientists agree with it.
• it has been supported by evidence from numerous
investigations and observations.
• it is first proposed as an explanation.
• it is published in a textbook.
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What is Life?
• What are some characteristics of life?
– Made up of cells
– Reproduce
– Based on universal genetic code
– Grow and develop
– Respond to environment
– Obtain and use materials and energy
– Maintain a stable internal environment
– Taken as a group, living things evolve
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What is Life?
• Which of these are alive?
– Virus?
– Protein?
– Fire?
– Computer virus?
– Mule?
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Me
Leroy
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19–2 Viruses
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What Is a Virus?
What Is a Virus?
Viruses are particles of nucleic acid, protein, and in some
cases, lipids.
Viruses can reproduce only by infecting living cells.
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What IsMosaic
a Virus?
Tobacco
Virus
RNA
T4 Bacteriophage
Head
Tail
sheath
DNA
Influenza Virus
RNA
Capsid
Tail
fiber
Membrane
envelope
Capsid
proteins
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Surface
proteins
What Is a Virus?
A typical virus is composed of a core of DNA or RNA
surrounded by a protein coat.
A capsid is the virus’s protein coat.
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Viral Infection
Viral Infection
Once the virus is inside the host cell, two different
processes may occur.
– Some viruses replicate immediately, killing the host cell.
– Others replicate, but do not kill the host cell immediately.
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Bacteriophage
Viral Infection
injects DNA into
bacterium
Bacteriophage DNA
forms a circle
Lysogenic Infection
Lytic Infection
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Viral Infection
Lytic Infection
In a lytic infection, a virus enters a cell, makes
copies of itself, and causes the cell to burst.
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Viral Infection
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Viral Infection
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Viral Infection
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Viral Infection
Lysogenic Infection
Other viruses cause lysogenic infections in which a
host cell makes copies of the virus indefinitely.
In a lysogenic infection, a virus integrates its DNA
into the DNA of the host cell, and the viral genetic
information replicates along with the host cell's
DNA.
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Viral Infection
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Viral Infection
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Viral Infection
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Viral Infection
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Retroviruses
Retroviruses
Retroviruses contain RNA as their genetic information.
When retroviruses infect cells, they make a DNA copy of
their RNA.
This DNA is inserted into the DNA of the host cell.
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Viruses that contain RNA as their genetic
information are known as
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prions.
oncoviruses.
retroviruses.
bacteriophage.
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The first type of virus to be studied was the
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bacteriophage.
tobacco mosaic virus.
influenza virus.
AIDS virus.
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Which of the following statements about viruses is
true?
• Viruses appear similar to bacteria when studied with a
light microscope.
• Viruses display the essential characteristics of living
things.
• Viruses can reproduce independently if they contain DNA.
• Viruses cannot reproduce unless they infect a living cell.
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A virus integrates its DNA into the DNA of the host
cell but remains inactive for a while in
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a lytic infection.
a lysogenic infection.
neither a lytic nor a lysogenic infection.
retroviral infection.
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Retroviruses are considered unique because
• they have RNA in their capsid and not DNA.
• they have DNA in their capsid and not RNA.
• after infection of a host cell, their RNA makes DNA.
• after infection of a host cell, their DNA makes RNA.
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