Experimental Design

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Experimental Design
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Hypothesis (Prediction)

• If (Manipulated/Independent Variable),
• Then (Responding/Dependent Variable).
• Example
• If Elodea is alone in water high in carbon
  dioxide (CO2), then the carbon dioxide (CO2)
  level will drop.

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Hypothesis Reason

• You should explain why you believe that a certain
  event will take place.
• The level will drop because plants take in carbon
  dioxide (CO2).

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Materials

• You must list all necessary materials to be used
  in the experiment.
• Example
• 2 jars with airtight lids
• distilled water
• a bromothymol blue (BTB) testing kit
• a straw
• an Elodea plant
• an aquatic snail

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2 Controlled Variables (kept the same)

• These variables are the bystanders in the
  experiment they are needed for the experiment to
  be completed, but they are not believed to have
  any measurable effect on the Responding Variable.
• Include at least two Controlled Variables.
• Be sure to label them as Controlled Variables!
• Examples
• 2 same size jars with airtight lids
• Equal volumes of distilled water
• The same straw

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Manipulated Variable (changed)

• Also called the Independent Variable. This is the
  thing that you believe will have a measurable
  effect on something else.
• Located between the If and the then.
• Examples
• Elodea in CO2 rich water

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Responding Variable (dependent)

• Also called the Dependent variable, this is the
  effect that is measured in the experiment.
• Carbon dioxide levels

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Record Measurements

• It should not be assumed that the WASL graders
  will know what you are thinking.
• Be certain to state (in words) that you will
• Observe (five senses, and tools)
• Record (on paper in a data table of some form).
• In the morning of day 4, replace the snail with
  the Elodea plant in Jar B. In the afternoon of
  the same day, observe both jars and record the
  color of the water in the data table.

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Repeated Trials

• Each experiment ought to be repeated several
  times. This is done for a few reasons
• Increase accuracy of each data record and to
  reduce possible sources of error
• Confirm whether the data are consistent from
  experiment to experiment.
• For example This experiment will be repeated a
  total of three times.

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Validity Measures

• When multiple trials (single experiments) are
  repeated, each additional trial must be exactly
  the same as all others.
• A simple way to communicate that you know this is
  important is to state any of the following
• Clean glassware before starting.
• Taking resting blood pressure between trials.

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Logical Steps

• Investigation Setup
• Procedure
• 1. Clean both jars and then fill the jars with
  equal amounts of water. Label them A and B on the
  morning of day 1.
• 2. Through a straw, exhale equally into both jars
  to create a high presence of carbon dioxide
  (CO2), replace the lids, and place both jars in
  sunlight.
• 3. In the afternoon, add 5 drops of bromothymol
  blue (BTB) to both jars and record the color of
  the water in the data table.
• 4. In the morning of day 2, add the Elodea plant
  to Jar B. In the afternoon of the same day,
  observe both jars and record the color in the
  data table.
• 5. In the morning of day 3, replace the Elodea
  plant with the snail in Jar B. In the afternoon
  of the same day, observe both jars and record the
  color of the water in the data table.
• 6. In the morning of day 4, replace the snail
  with the Elodea plant in Jar B. In the afternoon
  of the same day, observe both jars and record the
  color of the water in the data table.
• 7. In the morning of day 5, replace the Elodea
  plant with the snail in Jar B. In the afternoon
  of the same day, observe both jars and record the
  color of the water in the data table.

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Validity Controlled Variables Identifying
Variables Measurement

• If Elodea is alone in water high in carbon
  dioxide (CO2), then the carbon dioxide (CO2)
  level will drop. The level will drop because
  plants take in carbon dioxide (CO2).
• Materials 2 jars with airtight lids, equal
  amounts of distilled water, a bromothymol blue
  testing kit, a straw, an Elodea plant, equal
  amounts of CO2 bubbled into solutions

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Validity Controlled Variables Identifying
Variables Measurement

• Procedure
• 1. Clean both jars before the experiment and then
  fill the jars with equal amounts of water. Label
  them A and B on the morning of day 1.
• 2. Through a straw, exhale equally into both jars
  to create a high presence of carbon dioxide
  (CO2), replace the lids, and place both jars in
  sunlight from the same source.
• 3. In the afternoon, add 5 drops of bromothymol
  blue (BTB) to both jars and record the color of
  the water in the data table.
• 4. In the morning of day 2, add the Elodea plant
  only to Jar B, which will be the experimental
  group. In the afternoon of the same day, observe
  both jars and record the color in the data table.
• 5. Allow both jars to set over night. B. In the
  afternoon of the day 3, observe both jars and
  record the color of the water in the data table.
• 6. Repeat the experiment 3 times to collect
  additional data.

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Validity Controlled Variables Identifying
Variables Measurement
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Summary

• Use diagrams, words, pictures, and labels to
  communicate your ideas.
• Dont assume that the graders know anything about
  science (Experimental Design, etc.)
• Follow the Investigative Attributes to earn as
  many value points as possible.
• You need 7-10 Value points to pass!

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• Thank you Mr. Smith!