By Aryeh Gruber
The arthropods or Arthropoda constitute over 90% of the animal kingdom. They are distinguished from other animals by an exoskeleton, body divided into distinct parts, jointed legs and appendages, and bilateral symmetry (both sides of the body are the same). There are many classes or divisions of these animals. Arthropods occur in virtually every habitat, from the cold ocean depths to the hottest deserts. They can live through extremes that would kill most vertebrates. Depending on the class, arthropods are either herbivores or carnivores(predators). They are eaten by birds, reptiles, and fish.
The respiratory system is responsible for delivering sufficient oxygen to all cells of the body and for removing carbon dioxide that is produced as a waste product of cellular respiration. The respiratory system of arthropods is a complex network of tubes tracheal system that delivers oxygen to every cell. Air enters the insect's body through valve-like openings in the exoskeleton. These openings (called spiracles) are located along the thorax and abdomen of most insects. Next, air enters a tracheal trunk, eventually diffusing throughout a network of tracheal tubes that reach every part of the body. At the end of each tracheal branch, a cell (the tracheole) gives a thin, area for the exchange of gasses between air and the cell. Oxygen in the tracheal tube dissolves in the liquid of the tracheole. Carbon dioxide, produced as a waste product of cellular respiration, diffuses out of the cell and, eventually, out of the body through the tracheal system.