The role of DNA in cellular differentiation is to — A. provide a series of genes that can be turned on or off.
B. mutate genes when a cell divides in two.
C. produce mitochondria for energy production.
D. protect genes from damage as they reproduce.

thrombocytopenia, which is a deficiency in blood platelets, can cause bleeding and bruising in the dermis similar to senile purpura. other possible causes include: exposure to ultraviolet rays and aging skin are common causes of senile purpura. senile purpura may also be a sign of collagen loss in the skin and bones.