Answer is: cellular respiration creates an energy molecule when glucose is broken down.
Conservation of mass (mass is never lost or gained in chemical reactions), during chemical reaction no particles are created or destroyed, the atoms are simply rearranged from the reactants to the products.
The egg contains both food and mitochondria in addition to its vital DNA, thats why it is much larger. The sperm cell has to be much smaller than the egg cell, because it is the one that swims. If a sperm cell were as big as an egg, it would not be able to move very fast nor very far.
