1. Define Excretion.
  2. What are the 3 main groups of excretory wastes found in animals?
  3. Name the principal excretory organ in man. What does it excrete?
  4. Why is the right kidney lower than the left?

Dear Student, 1.Excretion is the process of removal of waste products from the body. Kidney is the chief excretory organ of the body. The skin and lungs are other important excretory organs of the body. 2. The 3 major groups of animal wastes are: i). Uricotelic - The organisms that excrete nitrogenous wastes as uric acid in the form of pellet or paste with a minimum loss of water are called uricotelic animals. Fr examples, Birds that cannot afford to loose water like humans or fishes, therefore they have developed a mechanism to excrete waste loosing least amount of water. Uric acid is only a little soluble in water and hence can be excreted by loosing only a small amount of water. ii).Ammonotelic - Those organisms which excrete nitrogenous wastes in the form of ammonia are called as ammonotelic. Ammonia is highly soluble in water and for its elimination a lot of water is required. Aquatic animals live in abundance of water and can afford to loose a lot of water as they would gain it very easily. So, aquatic animals are ammonotelic. iii). Ureotelic - Ureotelic animals are animals that excreate nitrogeenous wastes in the form of urea are called ureotelic. Urea requires less water to be eliminated than ammonia and hence it has become a feature of terrestrial animals like humans. 3. The principal excretory organs in man are i)The kidneys- The two kidneys excrete urine, which consists mainly of excess water, mineral salts and nitrogenous wastes from protein breakdown, urea and uric acid. ii)The lungs- The two lungs excrete carbon dioxide and water vapour. iii)The skin- The skin excretes sweat, which although more dilute, contains the same excretory substances as urine. Foreign substances can be excreted in the hair and the nails. iv)The liver- The liver plays a major part as it secretes bile. Bile has pigments made from broken-down haemoglobin in the red blood cells. The liver also detoxifies poisonous substances that may have entered the body through the alimentary canal. 4.The right kidney is lower than the left because of the organ that is anatomically above it, or superior to it, namely, the liver. The liver starts out larger on the right side of the body, and then tapers off to the left. Because the abdominal cavity is limited in space, the body had been designed by Nature to accommodate the large part of the liver by having the right kidney lower than the left. Regards

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