Vaccines are used for viral infections because

a) teach the body how to digest viruses in the intestines and dispose of them in waste (like feces)

b) vaccines are for bacterial infections not viral.

c) teach the memory b cells how to fight off infections

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.