When a woman goes into labor during childbirth, the cervix expands which sends a signal to the pituitary gland to release oxytocin which results in more contractions which results in more oxytocin being released and so on. what is happening during childbirth?

a negative feedback loop.
cell regulation
a positive feedback loop.
a neutral feedback loop

The answer is overmatching

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.