Excretion in animals
Excretion may be defined as the separation and elimination of the metabolic wastes from the body usually in an aqueous solu tion. The waste materials are of several kinds and vary not only from animal to animal, but also in the same animal from time to time. However, the term excretion is generally used with reference to the elimination of the nitrogenus waste products. from the animal body. During the oxidative metabolism of carbohydrates, carbon dioxide and water are formed as excretory products. The bile pigments bilirubin and biliverdin that are formed in the liver by the break down of haemoglobin are excretory substances which pass out through the intestine. The breakdown of proteins results in amino acids, the excess of which are excreted. While some aquatic animals excrete their extra nitrogen in the form of amino acids as such, most of the animals degrade their excess amino acids to ammonia, uric acid or urea. Deamination The first stage in the breakdown of amino acids ...