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“Research is what
I’m doing when I
don’t know what
I’m doing” – Werner von Braun (a German
aerospace engineer and one of
the leading figures in the
development of rocket
technology in Nazi Germany
during WWII and in the United
States after)
The
“Buzz” in
AP
Biology is
Inquiry
The Experimental Design
•
Step 1 - Define a Problem Based on
Observations and Background Research
Topic Statement – (briefly) captures the meaning of the research
Focused Research Question –this defines the whole process, guides your arguments and inquiry, and provokes the interests of the reviewer
Experimental Design –summarizes the method of research
Step 1 - Define a Problem Based on
Observations and Background Research
Hulley S, Cummings S, Browner W, et al. Designing clinical research. 3rd ed. Philadelphia (PA): Lippincott Williams and Wilkins; 2007.
Examples of a Focused
Research QuestionTopic: The distribution and growth of lichens on urban pavements
Research Question: How are the distribution and growth of lichens affected by sulfur dioxide and ozone levels in the atmosphere?
Experimental Design: Thalus diameter and population density data is collected from selected sites in different parts of the city. This data is then correlated with published data on the levels of sulfur dioxide and ozone.
Examples of a Focused
Research QuestionTopic: The effectiveness of commercial antibacterial cleaning agents
Research Question: Are commercially available antibacterial cleaning agents effective at controlling the growth of E. coli on nutrient agar under laboratory conditions?
Experimental Design : Pure strain E. coli are grown on nutrient agar plates under controlled conditions. Filter paper discssoaked in samples of the antibacterial agents are placed on the agar plates and the zone of inhibition (or exclusion) is measured and compared.
Step 2 - In order to formulate an answer to our problem we must design an experiment to test our hypothesis
Hypothesis - The tentative and testable explanation for an observation.
- should be explained.
- should be quantified
- should be written as an if/then/because statement
“If we knew what we were
doing, it wouldn’t be called
research, would it?”Albert Einstein
Critical Components of the Experimental Design
Critical Components of the Experimental Design•Independent Variable - The variable you
have control over, what you can choose
and manipulate;
What is varied in the experiment (for
example, time, pH, temperature,
concentration)
•Dependent Variable(s) - What you measure
in the experiment and what is affected
during the experiment (i.e. what the
investigator measures, counts, or records;
it is being affected in the experiment
•Controlled Variables - Variables that are
kept constant during the experiment
(variables not being manipulated)
Critical Components of the Experimental Design•Control Group or Control Treatment
- The treatment or set-up that
eliminates the independent
variable or sets it at a standard
value
-Positive controls : an experimental
treatment that will give the desired
result
-Negative controls: An
experimental treatment that will
yield a negative result
Other Critical Components of the Experimental Design
•Level of Treatment - The
appropriate values to use
for the independent
variable
•Replication - The number
of times the experiment
is repeated to verify the
results
Step 3 - Procedure/Protocol - The process
used to measure the dependent variable
(must be written so that it can be repeated
accurately)
Identify the variables in the following experiments. Underline the dependant
variable and circle the independent variable. Next, suggest a control treatment and list
at least 3 controlled variables
Height of bean plants growing at different
pH levels is recorded daily for 2 weeks.
CT
CV
CV
CV
Guinea pigs are kept at different temperatures for
6 weeks. Percent weight gain is recorded.
CT
CV
CV
CV
Percent absorption by the pigment chlorophyll is
measured for red, blue, green, and yellow
wavelengths of light.
CT
CV
CV
CV
Batches of seeds are soaked in salt solutions of different
concentrations, and germination is counted for each batch.
CT
CV
CV
CV
Scientific Method
Review Problem
Agricultural scientists were concerned about the
effect of air pollution, sulfur dioxide in particular,
on soybean production in fields adjacent to
coal-powered manufacturing plants. Based on
initial investigations, they proposed that sulfur
dioxide in high concentrations would reduce the
reproduction of soybeans. They designed an
experiment to test this hypothesis (see Figure
1). In this experiment, 48 soybean plants, just
beginning to produce flowers, were divided into
two groups, treatment and non-treatment. The
24 treated plants were divided into four groups
of 6.
One group of 6 treated plants was placed in a
fumigation chamber and exposed to 0.6 ppm
(parts per million) of sulfur dioxide for 4 hours to
stimulate sulfur dioxide emissions from a power
plant. The experiment was repeated on the
remaining three treated groups. The non-
treatment plants were placed similarly in groups
of 6 in a second fumigation chamber and
exposed to filtered air for 4 hours. Following
the experiment, all plants were returned to the
greenhouse. When the beans matured, the
number of bean pods, the number of seeds per
pod, and the mass of the pods were determined
for each plant.
a) For the soybeans, three dependent variables are measured, all of which provide information about reproduction. What are they? (3 points)
b) What is the independent variable in the experiment? (1 point)
c) Explain the importance of having only one independent variable. (1 point)
d) Why is it acceptable to have more than one dependent variable?
(1 point)
e) Name 7 controlled variables in this experiment. (7 points)
f) What is the level of treatment in this investigation? (1 point)
g) Describe how this investigation is replicated. (1 point)
Scientific Method
Review Solutions
a)For the soybeans, three dependent
variables are measured, all of which
provide information about reproduction.
What are they? (3 points)
-number of bean pods
-number of seeds per pod
-mass of pods
b)What is the independent variable in the
experiment? (1 point)
-sulfur dioxide
c)Discuss the importance of having only one
independent variable. (1 point)
-to determine the effect of that/one
particular variable only
-the need to know which factor is
affecting the dependent variable
d)Why is it acceptable to have more than
one dependent variable?
(1 point)
-each of the variables can be a way of
measuring the characteristic(s) being
affected
e)Name 6 controlled variables in this experiment.
(7 points)
-temperature -size of plants
-age of plants -variety of soybeans
-type of soil -pH of soil
-amount of fertilizer -amount of light
-water routine/amount
-day length -air flow
-humidity -etc.
f) What is the level of treatment in this
investigation? (1 point)
-0.6 ppm every 4 hours
g)Describe how this investigation is
replicated.
(1 point)
-the plants were divided into 4 groups
of 6 plants each and the entire
procedure was replicated 4 times.