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									Name _____________________________________________________            Date __________________      Biology

                                            EXPERIMENTAL VARIABLES

A variable is a factor that can change or be changed. In the situation described by the statement that “the height of
bean plants depends on the amount of water they receive”, there are many variables that could be identified. For
example, the height of the bean plant, the amount of water, amount and kind of fertilizer, amount and kind of light,
temperature, etc. Identify possible variables in the following statements:

    1.   The time it takes to run a kilometer depends on the amount of practice a person does.



    2. The higher the temperature of the water, the faster the eggs will cook.



    3. An experiment was done to see if keeping the lights on for different amounts of time each day affected the
       number of eggs chickens laid.



    4. The temperature of the water was measured at different depths of a lake.



    5. Grass will grow taller if it is watered and fertilized.




If a variable is deliberately changed in a situation by the experimenter, it is called the INDEPENDENT OR
MANIPULATED VARIABLE. It is the variable being tested by the experiment. Identify the independent variable in
the following situations:

    6. The amount of pollution produced by cars was measured using gasolines containing different amounts of
       lead.


    7. Lemon trees receiving the most water produce the largest lemons.



The variable in an experiment that changes because of the changes made with the manipulated variable is called the
DEPENDENT OR RESPONDING VARIABLE. In the example above, the size of the lemons would be the
dependent variable because the size changed as a result of the amount of water. Find the responding variable in the
following example:

    8. The number of potatoes depends on the amount of fertilizer used.



Identify the INDEPENDENT and DEPENDENT variables in the following examples:

    9. An investigation was performed to see if corn seeds would sprout at different times depending on the
       temperature of the water in which they were placed.

Independent _______________________________________________________
Dependent ________________________________________________________
    10. Five groups of rats were fed identical diets except for the amount of vitamin A. After three weeks, the rats
        were weighed to see if the amount of vitamin A had affected their weight.

Independent _______________________________________________________
Dependent _______________________________________________________

    11. An experiment was done with 6 groups of students to see if their scores on science tests were affected by the
        amount of studying they did each day.

Independent _______________________________________________________
Dependent _______________________________________________________

There is a third kind of variable which is carefully kept the same in all test groups. This type of variable is called a
CONSTANT OR CONTROLLED VARIABLE. Every scientist must give careful thought to controlling variables
every time he/she designs and experiment. To do that, ask three questions about each variable: what kind?, how
much?, and how often? In a controlled experiment, there can only be one variable tested (made different between the
test groups). If there is more than one variable changed in an experiment, the experimenter will not know which
variable caused the results. A good experiment has many controlled variables, only ONE independent variable and
usually only one dependent variable. Identify each type of variable in the following examples:

    12. Two groups of students were tested to compare their speed working math problems. Each group was given
        the same set of problems, same light, same temperature, same noise level. One group used calculators and the
        other group computed without calculators.

Independent _______________________________________________________
Dependent _______________________________________________________
Controlled Variables ________________________________________________

    13. Students of different ages were given the same puzzle to assemble. The time it took to assemble the puzzle
        was measured.

Independent _______________________________________________________
Dependent _______________________________________________________
Controlled Variables ________________________________________________


    14. An experiment was performed to determine how the amount of coffee grounds could affect the taste of coffee.
        The same kind of coffee, the same percolator, the same amount and type of water, the same perking time, and
        the same electrical source were used.

Independent _______________________________________________________
Dependent _______________________________________________________
Controlled Variables ________________________________________________

								
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