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Excretion in Animals

Excretion in Animals Synopsis



  • There are various metabolic activities which take place inside the living organisms. All these activities are chemical reactions which produces several end products that are of no use to the cells. These are called as wastes. 
  • These must be removed from the body for proper functioning of the body. The elimination of these waste nitrogenous products form the body is called as excretion. 
  • The excretory products include ammonia, urea, uric acid, carbon dioxide, pigments, salts digestive wastes, excess of water etc. These are removed from the body by different methods.

Excretion in Amoeba

  • Amoeba is a unicellular organism found in fresh water. 
  • In amoeba carbon dioxide and ammonia are the major waste materials. These waste materials are excreted out by the process of diffusion through general body surface.

  • In amoeba, contractile vacuoles also play some role in the removal of waste materials. 
  • The waste materials present in the cytoplasm of amoeba enters the contractile vacuole. Then the contractile vacuole moves close to the plasma membrane, comes in contact with plasma membrane and bursts to release its contents in the surrounding.
Excretion in Earthworm
  • Earthworm is ureotelic because its nitrogenous waste contains 40% urea, 20% ammonia, 40% amino acids, and other nitrogenous compounds. 
  • In earthworm carbon dioxide and nitrogenous wastes are the main waste materials. 
  • The carbon dioxide is excreted out from the body through its moist skin by the process of diffusion.
  • The nitrogenous wastes are excreted out of the body by special excretory organs called nephridia.
  • A nephridium is a tubular coiled structure. It starts from a rounded funnel shaped structure called nephrostome. The nephrostome opens in a coiled tube called nephridial tubule which is lined with cilia. The nephridial tubule opens outside the body through a small opening called nephridiopore.

  • In earthworms, the nephridia are classified into three types based on their location in the body-
  1. Septal nephridia: They are attached to the intersegmental septa. 
  2. Pharyngeal nephridia: They are found in three pairs, in tuft or bunch or either side of the alimentary canal in 4th, 5th and 6th segments.
  3. Integumentary nephridia: They are found scattered on the inner side of the skin or body wall in all segments except first 3 segments.

Excretion in Humans 
  • As a result of various metabolic process taking place inside the human body, a number of waste products are formed. These have to be eliminated as they are toxic to the body.
Excretory Substances
Excretory Organs

The Human Urinary System
The human urinary system consists of
  1. A pair of kidneys
  2. A pair of ureters
  3. Urinary bladder
  4. Urethra

Internal Structure of the Kidneys