Given a scientific question, generate a correct answer to it.

[EX Q]: What is continually released during childbirth through a positive feedback mechanism and prompts uterine contractions to fetal head toward the cervix?
[EX A]: oxytocin

[EX Q]: Negative feedback controls insulin secretion by what organ?
[EX A]: pancreas

[EX Q]: When an electron transitions from an excited state to a less excited state, or ground state, the difference in energy is emitted as a what?
[EX A]:
photon