scientific method

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Transcript scientific method

1.4 What Is Science?

Science is the systematic inquiry – through observation and
experiment – into the origins, structure, and behavior of living and
nonliving environments
1.4 What Is Science?

Science is based on the principle that all events have natural
causes

The belief that some events happen through supernatural forces (e.g.,
the actions of Greek gods)

The belief that all events can be traced to natural causes that we can
comprehend (natural causality)

Corollary: Evidence gathered from nature has not been deliberately
distorted to fool us
1.4 What Is Science?

The scientific method is an important tool of
scientific inquiry

The scientific method consists of six interrelated elements
 Observation
 Question
 Hypothesis
 Prediction
 Experiment
 Conclusion
1.4 What Is Science?

The scientific method is an important tool of scientific inquiry
(continued)

Scientific inquiry is a rigorous method for making observations

The scientific method for inquiry follows six steps
1.4 What Is Science?

The six steps of scientific inquiry
1. Observation of a specific phenomenon
2. The observation, in turn, leads to a question
3. The question leads to formulation of a hypothesis, based on previous
observations, which is offered as an answer to the question
1.4 What Is Science?

The six steps of scientific inquiry (continued)
4.
The hypothesis leads to a prediction, which is
the expected outcome of testing if the hypothesis is correct
5.
The prediction is tested by carefully designed additional observations
or carefully controlled manipulations called experiments
6.
The experiments produce results that either support or refute the
hypothesis, allowing the development of a conclusion
1.4 What Is Science?

Biologists test hypotheses using controlled
experiments

Two types of situations are established
A
baseline or control situation in which all possible
variables are held at a constant
 An
experimental situation in which one factor, variable,
is manipulated to test the hypothesis to determine that
this variable is the cause of an observation

Science is useless unless communicated
 The
scientific method is illustrated by experiments by
Francesco Redi and Malte Andersson
Figure E1-1 The experiment of Francesco Redi illustrates the scientific method
Observation: Flies swarm around meat left in the open; maggots appear on the meat.
Question:
Where do maggots on the meat come from?
Hypothesis:
Flies produce the maggots.
Prediction:
IF the hypothesis is correct, THEN keeping the flies away from the meat
will prevent the appearance of maggots.
Experiment:
Obtain identical pieces of
meat and two identical jars
Place meat
in each jar
Leave the jar
uncovered
Experimental variable:
gauze prevents the
entry of flies
Leave exposed
for several days
Controlled variables:
Flies swarm around
and maggots appear
Results
Control situation
Conclusion:
time, temperature,
place
Cover the jar
with gauze
Leave covered
for several days
Flies are kept from
the meat;
no maggots appear
Experimental situation
The experiment supports the hypothesis that flies are the source of
maggots and that spontaneous generation of maggots does not occur.
Figure E1-2 The experiment of Malte Andersson
Observation: Male widowbirds have extremely long tails.
Question:
Why do males, but not females, have such long tails?
Hypothesis:
Males have long tails because females prefer to mate with long-tailed males.
Prediction:
IF females prefer long-tailed males, THEN males with artificially lengthened tails will attract more mates.
Experiment:
Divide male birds
into four groups
Manipulate the
tails of the males
Do not
change the tail
Cut the tail and
re-glue in place
Experimental
variable:
Cut the tail to half of
the original length
Add feathers to
double the tail length
Release the males,
wait a week,
count the nests
Release the males,
wait a week,
count the nests
Average of less
than half a nest
per male
Average of
About two nests
per male
length of tail
Release the males,
wait a week,
count the nests
Release the males,
wait a week,
count the nests
Average of
about one nest
per male
Average of
about one nest
per male
Control groups
Conclusion:
Controlled
variables:
location, season,
time, weather
Results
Experimental groups
The hypothesis that female widowbirds prefer to mate with long-tailed males (and are less likely to mate
with short-tailed males) is supported.
1.4 What Is Science?

Scientific theories have been thoroughly tested

A scientific theory is a general and reliable explanation of important
natural phenomena that has been developed through extensive and
reproducible observations and experiments

A scientific theory is best described as a natural law, a basic principle
derived from the study of nature, which has never been disproven by
scientific inquiry
1.4 What Is Science?

Scientific theories have been thoroughly tested (continued)

The cell theory (that all living organisms are composed of cells) and the
theory of evolution are fundamental to the study of biology

Natural causality is the principle that all events can be traced to natural
causes

Natural laws apply to every time and place

Scientific inquiry is based on the assumption that people perceive
natural events in similar ways
1.4 What Is Science?

Scientific theories have been thoroughly tested (continued)

New scientific evidence may prompt radical revision of existing theory

For example, the discovery of prions
1.4 What Is Science?
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Scientific theories have been thoroughly tested (continued)

Before 1980, all known infectious diseases contained DNA or RNA

In 1982, Stanley Prusiner showed that the infectious sheep
disease scrapie is caused by a protein (a “protein infectious
particle,” or prion)
 Prions
have since been shown to cause “mad cow disease”
and diseases in humans
 The
willingness of scientists to revise accepted belief in light of
new data was critical to understanding and expanding the
study of prions
1.4 What Is Science?

Scientific theories involve both inductive and deductive reasoning

Inductive reasoning is used in the development of scientific theories

A generalization is created from many observations that support it and none
that contradict it

For example, the theory that Earth exerts gravitational forces on objects
began from repeated observations of objects falling downward toward Earth
and from no observations of objects falling upward away from Earth
1.4 What Is Science?

Scientific theories involve both inductive and deductive reasoning
(continued)

Deductive reasoning is the process of generating hypotheses based on
a well-supported generalization (such as a theory)

For example, based on the cell theory, any newly discovered organism
would be expected to be composed of cells
1.4 What Is Science?

Scientific theories are formulated in ways that can potentially be
disproved

Basic principles of science are referred to as theories because theories
can be disproved or falsified

Falsifying theories is distinctly different between scientific theories and
faith-based beliefs

“Each creature on Earth was separately created” cannot be subjected to
scientific inquiry because it is a belief rooted in faith
1.4 What Is Science?

Science is a human endeavor
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Human personality traits are part of “real science”

Scientists, like other people, may be driven by pride, ambition, or fear

Scientists sometimes make mistakes

Accidents, lucky guesses, intellectual powers, and controversies with
others contribute strongly to scientific advances
1.4 What Is Science?

Science is a human endeavor (continued)

In the 1920s, bacteriologist Alexander Fleming grew bacteria in cultures

One of the bacterial cultures became contaminated with a mold

Fleming was about to destroy the culture when he noticed the mold
(Penicillium) inhibited bacterial growth in the culture
1.4 What Is Science?

Science is a human endeavor (continued)

Fleming hypothesized that the mold produced an antibacterial
substance

Further tests using broth from pure Penicillium cultures lead to the
discovery of the first antibiotic, penicillin