Independent variable 鈥 the variable that is altered during a scientific experiment.
Dependent variable 鈥 the variable being tested or measured during a scientific experiment.
Controlled variable 鈥 a variable that is kept the same during a scientific experiment. Any change in a controlled variable would invalidate the results.
Example
Practical B2 - investigating the energy content of food
Independent variable 鈥 food sample.
Dependent variable 鈥 temperature increase of the water.
Controlled variables 鈥 mass of food, mass of water and distance of food to water.