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    Identifying Variables in Science Experiments, Part 2

    Using sample experiments, test yourself to see if you can identify independent, dependent, and controlled variables. Identifying variables is key in understanding and developing experiments. The questions are biology related, but this can be applied to any area of science.


    In any experiment, you can only have one independent variable. If you change more than one thing, then you do cannot be sure of what caused any changes that may have occurred.


    A study was done to determine if different amounts of phosphate in a fish tank affected the population of algae. The same size tank was used for each trial. Three tanks of identical size were used, and the amounts of phosphate added once a week for a month were as follows: tank 1 = 20 mg, tank 2 = 40 mg, tank 3 = 60 mg. What is the independent variable?


    What is the dependent variable?


    What is the controlled variable?


    John tested the temperature of the solution in his petri dish every three hours. What type of variable is the thermometer?


    What type of variable is the temperature of the solution?


    What type of variable is the time increments in which he took the temperature?


    If the amount of sugar added to water is increased, then the amount of hummingbirds attracted to the water will increase. What is the dependent variable?


    What is the independent variable?


    Which of the following does NOT have to be a controlled variable in order to keep this experiment valid?