When an organ (e.g. the heart) is controlled by two differen…

When an organ (e.g. the heart) is controlled by two different signal molecules, where one signal molecule activates the organ and the other signal molecule inhibits the organ, this is called a(n) ________ control system. Type the best answer that completes this sentence into the text box below:

If the concentration of a ligand decreases, the target cell…

If the concentration of a ligand decreases, the target cell may insert more receptors into the cell membrane.  This process, called _________, helps to keep the cell’s response at a normal level. Type the best answer that completes this sentence into the text box below: