Answer:
http://www.khalidshadid.com/uploads/3/9/2/0/3920808/raymond_chang-chemistry_10th_edition.pdf
Explanation:
http://www.khalidshadid.com/uploads/3/9/2/0/3920808/raymond_chang-chemistry_10th_edition.pdf
all cells come from pre existing cells
O is what should go in the blank. O stands for Oxygen.
Well it breaks down into small parts