What are the dependent, independent, and controlled variables in this experiment?

For a science project i have to test whether temperature affects the growth of seedlings. So i'm putting half of the seedlings in the fridge, and the other half outside. If it is possible could you also please explain what dependent, independent and controlled variables are? I really don't get it.What are the dependent, independent, and controlled variables in this experiment?
The easiest way to keep the independent/dependent variables straight is to remember that the letter ';D'; relates the DEPENDENT variable and the DATA that you are recording. In your example, the growth of the seedlings is the dependent variable since that is the DATA that you are recording, presumably as millimeters of plant height.





The independent variables are the conditions under which you are growing the plants such as the different temperatures, soils, nutrients, moisture, sunlight exposure, etc. In your case, the temperature of the environment is the independent variable.





However, as you've described your project, you have a problem with the lack of critical controlled variables. Presumably, the seedlings in the refrigerator will not be exposed to any sunlight whereas those grown outside obviously will. The controlled variables are all the variables that must be the same for both sets of plants except for the temperature. Both sets must have the same soil, nutrients, moisture AND sunlight exposure. Otherwise you will not be able to make any valid conclusions about the effect of temperature alone on the growth of the plants.





Perhaps you could devise a small greenhouse-like structure in which a refrigeration unit could maintain a constant temperature within it and placed outside near your ';outdoor'; plants grown under normal conditions. Maybe the cold air from the refrigerator could be ducted to the ';greenhouse';.





Oh, and one more thing -- soil moisture. The moisture in the warmer environment will evaporate faster than in the colder one. You'll need to monitor the soil moisture in both conditions and keep them the same.





Welcome to the challenging world of science. There are soooo many things to consider! :o)