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