Blood is a liquid that is present on all living things (except plants) which serves to deliver high levels of substances and oxygen is needed by the body's tissues, transporting chemicals results metabolism, as well as the body's defense against viruses or bacteria. Medical term pertaining to blood begins with the word hemo-or hemato-which comes from the Greece haima, meaning blood.
In insects, the blood (or better known as hemolimfe) is not involved in the circulation of oxygen. Oxygen is circulated through the system at the trachea form channels that transmit the air directly into the tissues of the body. The blood of insects transport the substances to the tissue and get rid of the rest of the metabolism.
In other animals, the main function of blood is to transport oxygen from the lungs or gills to the tissues of the body. The blood contained in hemoglobin that serves as the binding of oxygen. Most animals are not vertebrates or invertebrates that are small, direct oxygen seep into the blood plasma of dissolved oxygen carrier protein as freely. Hemoglobin is the oxygen-carrying protein is most effective and present on backboned animals or vertebrates. Hemocyanin, which is blue, containing copper, and is used by animal crustaceae. Squid use vanadium kromagen (colored light green, blue, orange or yellow).