What is the difference between an independent variable and a controlled variable?

Question

I know that an independent variable in an experiment is the variable that remains the same, and the dependent variable is the variable effected by the independent variable.

So, my question is.. if a controlled variable is a variable that remains "constant" or the same, what is the difference?

Answer 1

A controlled variable could change, but it will change the same for all treatments.  For instance, if you add different amounts of water to plants (independent variable) and measure growth (dependent variable) and you grow them in a greenhouse, the amount of light will be a controlled variable (the light will vary and it will affect plant growth, but it will affect the independent and dependent variable the same).  This way you can attribute changes you observe to the independent variable.

I hope that makes some sense.