A dependent variable in biology is an element that is being tested. It relies on the independent variable, or that aspect of the experiment that the scientist has control over and changes to observe the results on the dependent variable.
The dependent variable is an aspect in an experiment being tested by the scientist. The independent variable is altered, which in turn changes the dependent variable. For instance, if a scientist wants to observe the effects of light on a moth, the intensity of the light is changed. The light intensity is the independent variable; it is changed by the scientist. The effect of the different light intensities on the moth is the dependent variable. It depends on the light intensity or independent variable. When the independent variable changes, so does the dependent variable.
Another example of a dependent variable is in an experiment testing bone flexibility. A chicken bone is placed in a jar of vinegar. The independent variable is the vinegar. The dependent variable is what happens to the bone when it is placed in vinegar. After three days, the bone is removed and handled. Because of the vinegar, the calcium in the bone that makes it hard is gone, resulting in a soft, flexible bone.