Beta cells in the pancreas and human skin cells
both contain the insulin gene. the beta cells can
make insulin; however, skin cells cannot. which
process is responsible for this gene being
expressed in one cell type and not in another
cell type?
(1) mitosis (3) differentiation
(2) replication (4) meiosis

(3) differentiation 
In this process, the zygote, through the process of mitosis, becomes a muticellular organism where over time, the cells' DNA activate certain genes to express certain traits leading to the formation of tissues, then organs and even more complex structures resulting the formation of a fetus. 

Mitochondria is the cell organelle that produced the energy that is needed in the body system in form of atp, that is why it is called the power house of the cell. energy is needed by the living organisms to carry out the activities which sustain life.  if the mitochondria is destroyed atp will not be produced. if the mitochondria is destroyed, energy production will stop and the affected living organism will not have the energy to carry out the necessary life processes; this will lead to the death of the organism.