Which phytohormone promotes falling of old leaves whereas inhibits falling of young leaves?

Storage sprouting of potato tubers can be prevented by treatment with low concentrations of

Geotropic response is perceived by

Auxins are growth hormones capable of promoting cell elongation. They have been used in horticulture to promote growth,flowering,and rooting. Write a line to explain the meaning of the following terms related to auxins:
$(a)$ Auxin precursors
$(b)$ Antiauxins
$(c)$ Synthetic auxins

What is the mechanism underlying the phenomenon by which the terminal/apical bud suppresses the growth of lateral buds? Suggest measures to overcome this phenomenon.

Which hormone was first isolated from human urine?