Question

how do auxins promote the growth of a tendril around a support

Answer 1

because they are growth hormones in plants...

Answer 2

Explanation:

Auxin is a plant growth hormone. When the tip of the tendril touches a support, then the auxins present on its tip moves to the side of tip which is away from the support, so, due to more auxins in its tendrils away from the support grows faster.