Summary:
Leave a white flower in food dye to colour the vessels up the stem to the petals. (Or just use a petal.) The dye traces out the xylem vessels in the stem and branching vessels in the petals of the flower.
Science content (2016 curriculum):
Biology: Features, Adaptations of Living Things (K, 1, 3, 7)
Biology: Sensing, Organ Systems (4, 5, 6)