Once double fertilization occurs in plants, the zygote is and the endosperm is

Double fertilization happens when one sperm cell wires with the egg to create a zygote, and the other sperm cell wires with the two polar cores to make the endosperm. 
To answer the above:

Once double fertilization occurs in plants, the zygote is diploid and the endosperm is triploid.

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.

C) they are specialized meaning they are designed to do different things