For a flower to become an apple, the pollen that is produced by the flowers on one apple tree must be transferred to the flowers on another tree.
(a flower; to become; an apple) (the pollen; is produced; by the flowers) (the pollen that is produced by the flowers on one apple tree; must be transferred; to the flowers on another tree)
a flower the pollen the pollen that is produced by the flowers on one apple tree
to become is produced must be transferred
an apple
by the flowers
to the flowers on another tree