John had a science fair project that he needed to do. He wanted to test the effects that organic and chemical fertilizers had on plant growth. John predicted that the organic fertilizer would make the plants grow taller. He used three pots, three of the same type of seed, soil, organic fertilizer, chemical fertilizer, water, and a ruler. John put soil in the pots. He added chemical fertilizer to the first pot, organic fertilizer in the second pot, and no fertilizer in the third pot. He then planted one seed in each pot. John had to water the pots daily. He also checked for growth and took measurements for a period of 10 days. He measured the height of the plants. What are the controlled variable(s), independent variable, and the dependent variable?