What purpose is served by the loss of an -h and -oh end from two molecules as they join together during dehydration synthesis

To create positive and negative ends to attract and hence combine with each other.

Explanation:

Two molecules combine usually by some sort of attraction between them.

When one molecule loses OH- ion,  it becomes positively charges while the other molecule loses H+ ion and becomes negatively charged.

Now two molecules , one electro positive and other electro negative attracts each other and combine by forming hydrogen bonds.

Like wise the H+ and OH- released, also combines to form water.

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.