Entry #_____Name_________________________________________Date_________Period___
Experimental Design Reference
Scenario: A group of students is assigned a Populations Project in their Ninth Grade Earth
Science class. They decide to determine the effect of sunlight on radish plants. They grow 12
radish plants in 4" clay pots with 25 mL of water daily and 100 g of potting soil in 24 hours
darkness, 12 hours sunlight/12 hours darkness, and 24 hours sunlight. (They use Grow-Lights
to simulate sunlight.) After 5 days, they measure the height of all the plants in each pot.
1. Title: Must communicate what the experiment is about.
One good title: The Effect of (the independent variable) on (the dependent variable.)
Example: The Effect of Sunlight on the Height of Plants.
2. Hypothesis: Communicates what you think is going to happen in the experiment.
Always acceptable: If (the independent variable) is (increased, decreased, changed),
then ( the dependent variable) will (increase, decrease, change.)
Example: If the sunlight is increased, then the height of the plants will increase.
3. Independent Variable: (IV) (also called the Manipulated Variable) -- the variable you purposely
change or manipulate. Will be the CAUSE of the changes you measure.
Example: The sunlight
4. Dependent Variable: (DV) (also called the Responding Variable) -- the variable you will measure
after the experiment is set up. Will be the EFFECT of the action you took.
Example: The height of the plants
5. Constants:
All the other variables that remain the same for all the trials – otherwise they could affect the
results (they could ALSO change the dependent variable) and distort the connection between your
ONE IV and the DV.
Example: 4" pots, 100 g potting soil, 25 mL water daily
6. Control: The group that does NOT contain the independent variable -- -the no treatment group
or normal treatment group. Helps establish a baseline result that you can compare with your
experimental groups.
Example: the plants that receive 12 hours sun/12 hours dark (which best simulates real life)
– this will allow you to compare the results for the experimental plants growing in 24 hours
darkness and 24 hours sunlight
7. Trials: The number of times the experiment is repeated. The more times you can repeat the
experiment and get the same results, the more valid your conclusions are.
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Entry #_____Name_________________________________________Date_________Period___
Design Detective
Analyze each scenario below. For each scenario, make a list of the independent variable,
dependent variable, control, constants, number of trials, and suggestions for
improving the experimental design.
Scenario 1: Compost and Bean Plants
After studying about recycling, members of John's biology class investigated the effect of various recycled
products on plant growth. John's lab group compared the effect of different aged grass compost on beans
plants. Because decomposition is necessary for release of nutrients, the group hypothesized that older grass
compost would produce taller bean plants. Three flats of bean plants (25 plants/flat) were grown for five days.
The plants were then fertilized as follows: (a) Flat A: 450 grams of 3-month-old compost, (b) Flat B: 450
grams of 6-month-old compost, (c) Flat C: 0 grams of compost. The plants received the same amount of
sunlight and water each day. At the end of 30 days the group recorded the height of the plants (cm).
Scenario 2: Fossils and Cliff Depth
Susan observed that different kinds and amounts of fossils were present in a cliff behind her house. She
wondered if changes in fossil content occurred from the top to the bottom of the bank. She marked the bank
at five positions: 5, 10, 15, 20 and 25 meters from the surface. She removed one bucket of soil from each of
the positions and determined the kind and number of fossils in each sample.
Scenario 3: Aloe vera and Planaria
Jackie read that Aloe vera promoted healing of burned tissue. She decided to investigate the effect of
varying amounts of Aloe vera on the regeneration of planaria. She bisected the planaria to obtain 10 parts (5
heads and 5 tails) for each experimental group. She applied concentrations of 0%, 10%, 20%, and 30% Aloe
vera to the groups. Fifteen ml of Aloe vera solutions were applied. All planaria were maintained in a growth
chamber with identical food temperature, and humidity. On Day 15, Jackie observed the regeneration of the
planaria parts and categorized development as full, partial, or none.
Scenario 4: Spilled Milk
Susie wondered if the height of a hole punched in the side of a milk carton would affect how far from the
container a liquid would spurt when the carton was full of the liquid. She used 4 identical milk cartons and
punched the same size hole in each. The hole was placed at a different height on one side of each of the
containers. The height of the holes varied in increments of 5 cm, ranging from 5 cm to 20 cm from the base of
the carton. She put her finger. over the holes and filled the cartons to a height of 25 cm with water. When
each carton was filled to the proper level, she placed the carton in the sink and removed her finger. Susie
measured how far away from the carton's base the liquid had squirted when it hit the bottom of the sink.
Scenario 5: Wax On, Wax Off!
Jack wanted to test which brand of car wax was the most effective. He tested four brands of wax. He cleaned
the hood of his car and removed the old wax. He measured four equal sections on the hood of the car. Each of
the waxes was used to cover a section. An equal amount of wax, the same type of rag, and equal buffing were
used. Five drops of water were placed on each square and the diameter of each drop was measured.
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Entry #_____Name_________________________________________Date_________Period___
Experimental Design Detectives
Independent
Variable
Dependent
Variable
Control
Constants
Number
of Trials
Improvements
1.
2.
3.
4.
5.
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