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Controls and Variables (Grade 9)

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Controls and Variables

For an experiment, a scientist put lime at the base of tomato plant A and baking soda at the base of tomato plant B. She then sealed the plants in plastic bags. Tomato plant A eventually died, and tomato plant B stayed healthy.

What was the dependent variable in this experiment?
  1. type of plant grown for the test
  2. response of the plants to each substance
  3. substance at the base of each plant
  4. plastic bags wrapped around each plant
What is the difference between a control group and an experimental group?

Why do experiments usually test only one variable at at time?

The                      is used in an experiment to show that the results of an experiment are actually a result of the condition being tested.
  1. independent variable
  2. control
  3. hypothesis
  4. dependent variable
The factor in an experiment that is manipulated is the
  1. independent variable.
  2. constant.
  3. hypothesis.
  4. dependent variable.
The factor in an experiment that can change if other factors are changed is the
  1. independent variable.
  2. constant.
  3. hypothesis.
  4. dependent variable.
Mr. Krabs wants to test whether or not his secret ingredient for breath mints will cure the bad breath people get from eating crabby patties. He conducted an experiment on 100 customers. Mr Krabs had 50 customers (Group A) eat a breath mint with his secret ingredient after eating a crabby patty . The other 50 customers (Group B) were given a regular breath mint without the secret ingredient. Both groups were told that they were getting the breath mint and that it would cure their bad breath. Two hours after eating the crabby patties and mints, 30 customers from Group A and 10 customers from Group b reported having better breath than they normally had after eating crabby patties.

Which group is the control group?

What is the independent variable?

What is the dependent variable?

Why do you think 10 people in Group B reported fresher breath?

Bob noticed that his favorite pants were not as clean as they used to be. Sandy told him to try using a new brand of laundry detergent called Clean-O. Bob washed one pair of pants in plain water and another pair in water with the Clean-O detergent. After washing both pairs a total of three times, the pants washed in the Clean-O did not appear to be any cleaner than the pants washed in plain water.

What was the problem Bob wanted to investigate?

What is the independent variable?

What is the dependent variable?

What should Sponge Bob's conclusion be?

A botanist wants to see how different colored light waves influence the growth of pea plants. She puts the same number of seeds into three identical pots with the same kind and amount of soil. She then gives them the same amount of water every three days for the length of the experiment. One pot is placed into a dark windowless closet. Another pot is left on the windowsill, and the third is placed under a lamp with a green bulb. She records the height of each plant every day for three months.
What is the independent variable in this experiment?
  1. the amount of soil in the pots
  2. the color of the light given to the plants
  3. the amount of water given to the plants
  4. the amount of time the experiment was conducted
In an experiment investigating the effects of color on birdhouse selection by sparrows, which situation could be a control?
  1. a birdhouse that is red in color
  2. a birdhouse that has a very large opening
  3. a birdhouse that has not been painted
  4. a birdhouse that is located near a food source
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