Does one pollen grain produce one seed, and if so..?

[zedd]

I am very confused about certain aspects of pollination. Does 1 pollen grain equal 1 seed? Some people tell me a fertilised ovule will multiply into many seeds, others say one pollen grain + 1 egg = 1 seed (and thus 1 seedling). If each pollen grain contains 2 sperm cells, as some sources state, does this mean each pollen grain splits into 2 seeds? If only 1 grain of pollen enters the stigma, how come when an ovary is split many seeds might be produced? How come a pepper or an apple if split open will reveal large numbers of seeds? Can these all be replanted to grow? Does an ovary only bear several seeds if the flowerhead contains more than one stigma? Most of the flower heads I see have a single stigma. I wonder if this means only one seed appears in the ovary. For instance, Viscum album produces usually a single seed within its fruit. Is this so with all monocarpous plants?