The nitrogen compounds through which toxic nitrogen is eliminated from organisms are ammonia, urea and uric acid. All of these substances are produced from protein metabolism. Ammonia(NH 3) forms with the oxidation of amino groups (NH 2), which are removed from the proteins when they convert into carbohydrates.ll the metabolic wastes are excreted in a form of water solutes through the excretory organs (nephridia, Malpighian tubules, kidneys), with the exception of CO 2, which is excreted together with the water vapor throughout the lungs.