For culturing of cells, medium is typically supplemented with serum (e.g. fetal bovine serum or FBS) at 10%-15% of the total volume. The serum provides growth factors and cytokines that stimulate cells to survive and proliferate.
Consider the following experiment where normal cells and cancer cells are cultured in the presence or absence of serum over the time course of several days, and cell counts are determined. The figure represents that data obtained from such an experiment with 4 different groups.
Which of the following plots would represent cancer cells grown in the absence of serum?