Answering Scientific Questions

Answering Scientific Questions
Sarah Redd
Scientists use inquiry in their study of
nature
• The word Science is derived from Latin and
means “to know”
• Science distinguishes itself from other ways of
knowing by requiring evidence
Inquiry = the process of inquiring, asking
questions about the way the world works
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
What kinds of questions can science
answer?
• To be scientific, a question must:
– Be specific and well-defined
– Be testable
– Be possible to control confounding factors (to
some extent) and measure some kind of result
Are these questions scientific?
• Does alcohol consumption cause people to
behave immorally?
• Does bright coloration reduce predation on
monarch butterflies?
• Do inferior parents contribute to a lower adult
job salary in their children?
• Does wearing sunscreen prevent skin cancer?
• Does drinking coffee make it easier to stay
awake?
• Should genetically modified salmon be sold in
grocery stores?
The Role of Hypotheses in Inquiry
• A hypothesis is a tentative answer to a scientific
question (like an educated guess)
• A hypothesis is generally worded in the format
_______________ affects _______________.
• When you write the hypothesis, the verb doesn’t
have to be “affects.” It could be something like
increases, decreases, reduces, causes, etc.
• A scientific hypothesis leads to predictions that can
be tested by observation or experimentation
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Practice making hypotheses
Make hypotheses based on the following
questions:
• Does bright coloration reduce predation on
monarch butterflies?
• Does wearing sunscreen prevent skin cancer?
• Does drinking coffee make it easier to stay
awake?
• For example,
– Observation: Your flashlight doesn’t work
– Question: Why doesn’t your flashlight work?
– Hypothesis 1: Dead batteries are preventing your
flash light from working
– Hypothesis 2: A burnt out bulb is preventing your
flash light from working
• Both these hypotheses are testable
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 1-24
Observations
Question
Hypothesis #1:
Dead batteries
Prediction:
Replacing batteries
will fix problem
Hypothesis #2:
Burnt-out bulb
Prediction:
Replacing bulb
will fix problem
Test prediction
Test prediction
Test falsifies hypothesis
Test does not falsify hypothesis
A Closer Look at Hypotheses in
Scientific Inquiry
• A hypothesis must be testable and falsifiable
• Failure to falsify a hypothesis does not prove
that hypothesis is correct
– For example, you replace your flashlight bulb, and it
now works; this supports the hypothesis that your
bulb was burnt out, but does not prove it (perhaps
the first bulb was inserted incorrectly)
You can REJECT or FAIL TO REJECT a hypothesis, but
never prove it is true.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
A Case Study in Scientific Inquiry:
Investigating Mimicry in Snake
Populations
• Many poisonous species are brightly colored,
which warns potential predators
• Mimics are harmless species that closely
resemble poisonous species
• Henry Bates hypothesized that this mimicry
evolved in harmless species as an evolutionary
adaptation that reduces their chances of being
eaten
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Biologists David and Karin Pfennig and William
Harcombe tested this hypothesis with the
poisonous eastern coral snake and its mimic the
nonpoisonous scarlet kingsnake
• Both species live in the Carolinas, but the
kingsnake is also found in regions without
poisonous coral snakes
• If predators inherit an avoidance of the coral
snake’s coloration, then the colorful kingsnake
will be attacked less often in the regions where
coral snakes are present
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 1-25
Scarlet kingsnake (nonpoisonous)
Key
Range of scarlet
kingsnake only
Overlapping ranges of
scarlet kingsnake and
eastern coral snake
North
Carolina
South
Carolina
Eastern coral snake
(poisonous)
Scarlet kingsnake (nonpoisonous)
Field Experiments with Artificial Snakes
• To test this mimicry hypothesis, researchers
made hundreds of artificial snakes:
– An experimental group resembling kingsnakes
– A control group resembling plain brown snakes
• Equal numbers of both types were placed at
field sites, including areas without poisonous
coral snakes
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 1-26
(a) Artificial kingsnake
(b) Brown artificial snake that has been attacked
• After four weeks, the scientists retrieved the
artificial snakes and counted bite or claw marks
• The data fit the predictions of the mimicry
hypothesis: the ringed snakes were attacked less
frequently in the geographic region where coral
snakes were found
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 1-27
RESULTS
Percent of total attacks
on artificial snakes
100
84%
83%
80
60
40
20
17%
16%
0
Coral snakes
absent
Coral snakes
present
Artificial
kingsnakes
Brown
artificial
snakes
Designing Controlled Experiments
• A controlled experiment compares an
experimental group (like the artificial kingsnakes)
with a control group (the artificial brown snakes)
• Ideally, only the variable of interest (the color
pattern of the artificial snakes) is different between
the control and experimental groups
• A controlled experiment means that control groups
are used to cancel the effects of unwanted
variables
• A controlled experiment does not mean that all
unwanted variables are kept constant
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The Scientific Method
• The scientific method is an idealized process
of inquiry
• Hypothesis-based science is based on the
“textbook” scientific method but rarely
follows all the ordered steps
• Discovery-based science has made
important contributions with very little
dependence on the scientific method
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
What is a scientific theory?
• In the context of science, a theory is:
– Broader in scope than a hypothesis
– General, and can lead to new testable hypotheses
– Supported by a large body of evidence in comparison to
a hypothesis
– Examples: Gravitational Theory, Evolutionary Theory,
Theory of Relativity
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Science, Technology, and Society
• The goal of science is to understand natural
phenomena
• The goal of technology is to apply scientific
knowledge for some specific purpose
• Science and technology are interdependent
• Biology is marked by “discoveries,” while
technology is marked by “inventions”
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• The combination of science and technology has
dramatic effects on society
– For example, the discovery of DNA by James Watson
and Francis Crick allowed for advances in DNA
technology such as testing for hereditary diseases
• Ethical issues can arise from new technology,
but have as much to do with politics,
economics, and cultural values as with science
and technology
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
An Example:
• Many people in the United States take vitamin
C supplements with the belief that they will
prevent disease. Does supplemental vitamin C
prevent illness?
Forming a hypothesis
 A hypothesis is a factual statement that can
be tested
 Write it in the form ____________ affects
____________.
 A hypothesis must be falsifiable
 One can reject or fail to reject a hypothesis, but
never accept it as known truth
Write a hypothesis about example question: Does
supplemental vitamin C prevent illness?
Hypothesis test: the variables
• The dependent variable is what the scientist
measures or observes in response to the
experimental conditions. In a standard format
hypothesis, this is whatever is in the second
blank.
• The independent variable is the experimental
condition that the scientist manipulates in order
to look for a response. In a standard format
hypothesis, this is the thing in the second blank.
• What are the variables in the Vitamin C example?
Designing the procedure
• Many experiments will utilize different levels of
treatment for the independent variable.
– So, we might give different amounts of vitamin C to our
participants
 A control group is one of the treatment levels where
everything is the same as your treatment of interest
except the thing that you think causes a response. This
allows a scientist to determine whether results are
really due to the independent variable.
 A control for our Vitamin C experiment would be people
who were given an unmedicated pill that looked just like
the Vitamin C pills, but contained no Vitamin C.
Experimental Units and Controlled
Variables
• Treatments are applied to experimental units.
– Who/what are we giving the treatment (Vitamin C)
to? They’re the experimental units.
– Replication is the number of experimental units in
each level of treatment. Without replication, your
results could be a random fluke!
• Controlled variables are things that the scientist
keeps constant in all the treatment groups in
order to avoid introducing error into the
experiment
– Having controlled variables is not the same as having a
control group.
One possibility…
Treatment Levels
Control (fake pill)
500 mg C / day
1000 mg C / day
2000 mg C / day
Person 1
Person 8
Person 15
Person 22
Person 2
Person 9
Person 16
Person 23
Person 3
Person 10
Person 17
Person 24
Person 4
Person 11
Person 18
Person 25
Person 5
Person 12
Person 19
Person 26
Person 6
Person 13
Person 20
Person 27
Person 7
Person 14
Person 21
Person 28
Plan: For 6 months, have each person keep a journal of the
number of days they feel sick. Define symptoms of
sickness very clearly to minimize differences in individual
interpretation.
Making predictions
• Scientists predict the results of their experiments using
“if then” statements
• “If the independent variable influences the dependent
variable, then I expect __________________.”
• Same as “If my hypothesis is true then I expect
_____________ to happen in the experiment.
• “If vitamin C prevents illness, then I expect people who
take the most vitamin C to have the smallest number of
sick days.”
Interpreting results
Number of sick days
• Results are often subjected to statistical
methods and graphed with the independent
variable on the x-axis and the dependent
variable on the y-axis.
Prediction
Amount of Vitamin C taken daily
How does science research work in
the “real world”?
• Most research
scientists work in
labs at universities
or companies
• Labs are commonly
home to graduate
students, post-docs,
lead researchers,
lab managers, and
technicians
Your lab is like a team.
• Usually, everyone has their own project
• Most labs hold regular meetings to see
how everyone is doing and give
suggestions when someone runs into
problems
• Lab members often show each other data
and practice research presentations for
their lab members before presenting to a
larger audience
Good research is peer reviewed
 In order to have their work respected, research
scientists try to publish their work in peerreviewed journals
 Before the journal accepts your paper, they send
it to scientists who know about your field
 Those scientists evaluate whether they think
your research is good enough for publication,
and give recommendations to the journal
 The journal may accept or reject your paper, or
send it back to you to fix some things or do extra
experiments before reviewing it again.
Some journals are more prestigious
than others…