Suppose some female rats are given caffeine and others are not. the researchers then count how many times the rats given caffeine couple with males and how many times the rats not given caffeine couple. in this example the independent variable is

The independent variable is that in which the result is dependent on. For experiments, this is usually the item being varied. For this case, what is being varied is that one group is given caffeine while the other is not. That makes the amount of caffeine given to be our independent variable. 

The answer would be simply interphase and mitosis