Why are taste and smell receptors classified as chemoreceptors?

Because they respond chemicals in aqueous solution. They have to react to saliva and that's why if you have a dry toungue they have nothing to react to.

There would be one bar shorter than the bar for peaches.

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.