Apoptosis is the process where damaged cells commit suicide to replace themselves with new cells. If damaged cells are not replaced then diseases, like cancer, can form.
Required Reading
Apoptosis: a basic biological phenomenon with wide-ranging implications in tissue kinetics by JF Kerr, AH Wyllie & AR Currie (The original research paper on apoptosis)
Developmental apoptosis in C. elegans by Guillaume Lettre and Michael O. Hengartner (A review on apoptosis in worms)
Bcl-2 gene promotes haemopoietic cell survival and cooperates with c-myc to immortalize pre-B cells by David L. Vaux, Suzanne Cory & Jerry M. Adams (Connects failing apoptosis to cancer)
Differential Equations 