| − | Special structures or chemicals that allow living organisms to sense the conditions of their surroundings.<ref>Wile, Dr. Jay L. ''Exploring Creation With General Science''. Anderson: Apologia Educational Ministries, Inc. | + | Special structures or chemicals that allow living [[organism]]s to sense the conditions of their surroundings.<ref>Wile, Dr. Jay L. ''Exploring Creation With General Science''. Anderson: Apologia Educational Ministries, Inc. |