The basic functions performed by living organisms to maintain their life on this earth are called life processes.
They are nutrition, respiration, transportation, circulation and excretion etc.
There are large number of chemical reactions that take place inside a living body. As a result, a variety of waste products are constantly being generated. The living body needs to remove these wastes. Excretion is the removal of metabolic waste products from the body.
Excretion in Unicellular and Multicellular Organisms:-
Unicellular Organisms:- Remove wastes by diffusion from the body surface into the surrounding water.
Multicellular Organisms:- Remove wastes from body by specialised organs.
Excretion in Human Beings:The main function of human Excretory system is to remove the nitrogenous waste such as urea or uric acid from the body. It includes a pair of Kidneys, a pair of Ureters, a Urinary Bladder and a Urethra. The purpose of making urine is to filter out waste products (urea or uric acid) from the blood. These wastes are removed from the blood by Kidneys and are passed down to the Urinary bladder by a pair of Ureters. Then through Urethra urine is thrown out of the body.
Nephron, the filtration unit of Kidney:
Formation of Urine:- Urine is formed in the body by following process.
Removal of urine: The urine formed in the kidney enters the ureter, from ureter it is stored in the bladder until the pressure of the expanded bladder leads to the urge to pass it out through urethra .