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

Example Input: What is the term for a loop in which a product feeds back to control its own production?
Example Output: feedback mechanism

Example Input: Activated macrophages and neutrophils discharge what that signals molecules that enhance an immune response?
Example Output: cytokines

Example Input: What model of the atom features an electron orbiting a nucleus, forming a closed-current loop and producing a magnetic field with a north pole and a south pole?.
Example Output:
planetary model