Which is not an example of a structural adaptation in plants?

a.
special leaves that open and close like jaws

b.
roots that grow in the direction of a water source

c.
seeds with a thick outer covering

d.
brightly colored flowers to attract pollinators

The correct answer is B. roots that grow in the direction of a water source

This is not about structural support but rather about searching for nutrients. It's a behavioral, functional adaptation, not a structural one. 

By water evaporation from the leaves is created a negative pressure at the top of the tree that promotes the ascension  of the water through channels that are called xylem. there are also two molecule forces that are involved: the intra-water molecules cohesion (water molecules stick to each other) and the adhesion when the water molecules stick to the channels they are running in. this is what enables water to go from the roots to the top of a tall tree.