The answer is to decrease the secretion of substances from the pituitary gland that cause growth.
Gigantism is condition characterized by excessive growth. It is the consequence of over-production of growth hormone (somatotropin) in the pituitary gland. So, the effect of the drug used on patients diagnosed with gigantism must be to decrease the secretion of growth hormone in the pituitary gland. That way, there will be less of growth hormone, and the excessive growth can be stopped.
Oxygen and carbon dioxide travels to and from tiny air sacs in the lungs, through the walls of the capillaries, into the blood. Blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs.
Natural selection is when the organisms that have the better adaptation so they survive. In this case, the green was the better adaptation so they lived.
