Final answer:
Molecules in area B of the endocrine system are principally used as enzymes or hormones, which are made of amino acids and help catalyze reactions and regulate bodily functions.
Step-by-step explanation:
The molecules that belong in area B are used mainly as enzymes or hormones, given that organs A and B are part of the endocrine system. These molecules, typically made of amino acids, are crucial for catalyzing biochemical reactions by lowering the activation energy needed for these reactions to occur. Also, they play a substantial role in signaling and regulation throughout the body. Molecules like amino acids and nucleotides absorbed by cells can be involved in energy production through cellular respiration or can be reassembled into larger molecules needed for various cellular functions.