I believe that substance would be water.
Mitosis happens in all types of cells. in this division, the cell will double it's number of chromosomes and then will be divided into two separated cells. so the number of chromosomes in product is equal to the number of chromosomes of the first cell
but meiosis only happens to produce gametes. the cell will be divided into two separated gametes.
in this division the number of chromosomes won't be doubled. so gametes have the half number of a normal person chromosomes.
good luck
