Excretion is a biological process by which an organism gets rid of excess or toxic waste products of metabolism. osmoregulation is a process that maintains the amount of water and proper ionic balance in the body.

Importance of Excretion and osmoregulation

  • Excretion removes the unwanted by products of metabolic pathways.
  • Excretion removes many toxic chemical substances which damage the cells act as enzyme inhibitors. It regulates the water content of body fluids which is very important in maintaining the solute potential and volume of body fluids.
  • Excretion is a very important process in regulating the pH of the body fluid. The PH of urine varies between 4.5 and 8.

Excretion in Plants

Plants are the producers and they synthesise all their organic requirements according to demands. Wastes substances, if produced in metabolic process of plants are disposed of by following methods:

  • Many breakdown products are recycled in the synthesis of new metabolic products.
  • Excess salt is removed through hydathodes along with guttation water.
  • Most of the toxic waste products are stored within dead permanent tissues such as heart wood, leaves or bark which are removed periodically.

Major waste substances produced by certain metabolic activities of plants are oxygen, carbon-di-oxide and H2O. CO2 and H2O are used by process of photo synthesis. The O2 which inhibit photo-synthesis in higher concentration escapes from plants into the environment by diffusion.

  • Some waste substances are eliminated through the petals, fruits and seeds.
  • Some excretory products such as latex, resin ducts store resin (resin of pine trees yields turpentine), mucilage duct store mucilage, oil glands store essential oil, etc.

Excretion in Animals

  • In amoeba waste materials CO2 is removed by diffusion through the cell membrane, but nitrogenous waste (like ammonia) and excess water are removed by the contractile vacuole.
  • In earthworm, tubular structures called the nephridia are excretory organs. In addition nephridia, moist skin of earth worm also acts as an excretory organ.
  • In human beings, microscopic thin tubules form nephron, which functions as excretory unit. About 1 million nephrons taken together form the excretory organ of human beings called kidney. Major waste products of human are CO2 and urea produced as by the decomposition of unused proteins in the liver. More of its accumulation may poisonous for body and can harm us, so its removal is the essential point. Lungs of human responsible for the removal of carbon-di- oxide while kidney responsible for removal of harmful substances as urea through the body in the form of urine.


 Excretory system of Human remains located in the abdominal cavity and consists of two kidney, two ureter, bladder and urethra.

Kidney of human is bean  shaped and function is to remove the poisonous  substance urea, other waste salts and excess water from blood and excrete them in form of yellow liquid called urine it is due to the presence urochrome pigment in urine. Thus kidney helps in filtering the blood and removes the toxic wastes in the form of urine throughout the body. Each of kidneys made up of large no of unit called.

Nephron: Each nephron consists of two parts. Malpighian body and tubular parts. And glomerulous while tubular portion consists of P.C.T. Loop of henel and the D.C.T. (Distal convulated tubules).

The blood in the capillaries of glomerulous comes from the aorta via renal arteries & after passing through glomerulous it returns to posterior vena cava via renal veins.

Blood entering into the glomerulous carries wastes material which is filtered out in the Bowman’s capsule. Wall of glomerular capillaries and bowman’s capsule are very thin are the selectively permeable. Once the waste material is filtered out, blood free from these waste materials goes into the renal veins from where it goes into heart. Fluid containing waste materials is forced out of the glomerular capillaries in the Bowman’s capsule.

The filtered out fluid is known as the glomerular filtrates which contains Na, K & C l, glucose, A. Along with urea, uric acid and large amount of water. During flow of glomerular filtrates usual substances reabsorbed and secretion of certain substances takes place fluid reaches the end of collecting duct is called urine. Human urine contain about 95% water and 5% nitrogenous substances (urea, uric a) finally urine passes through ureter and collects in bladder till thrown out of body by urethra.

Osmoregulation – It is the process of the regulating ion concentration and water content in the body. kidneys not only functions to remove toxic waste, but also act as osmoregulatory organs by controlling the water balance and levels of mineral-ions in the body.

The efficiency of kidney gradually declines with the increase of age. Its activity decline to about 50% by age of 70 in human being. Other cause of decline its function is kidney infection, injury related to blood flow. This will causes the kidney damage or mol functioning. Term for decline in its performance due to a disease called kidney failure.

There two alternative for kidney failure persons.- A matching kidney from a healthy person may be transplanted. An artificial kidney machine may be employed in order to get rid of metabolic wastes from the blood and to maintain normal levels of H2O and mineral ions in body fluid. Artificial kidney work on principle of natural kidney and procedure is called Dialysis. Finally cleaned blood is pumped back to the patient.

During dialysis heparin (As an anticoagulant substance) adds into blood to prevent clotting.


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