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Explain excretion in human beings in detail for 5 marks |
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Answer» Excretory system contain a pair of kidney ,two ureters ,a urinary bladder and a urethra .The unit of kidney is nephron . Kidneys are most important part of excretory system.There are two main steps for urine formation :1. Ultrafiltration of blood:The blood present in glomerulus is rich in nitrogenous waste .It is filtered out across the capilary wall and wall of Bowman\'s capsule.2.Reabsorbtion of useful substances :After filtration useful substances like glucose ,amino acid,excess water are re absorbed by tubule .After re absorbtion only urea ,uric acid ,some unwanted salt and some amount of water is left behind in tubule . This liquid form is urine .Urine is slightly acidic ,pale coloured liquid which contain water ,urea ,uric acid and some salt.3. Secretion: The urine is secreted into the tubule which open up into collecting duct and then into ureter. \tA pair of kidneys, a pair of ureters, a urinary bladder and a urethra constitutes the human excretory system.\tKidneys are present on either side of the backbone in the abdomen.\tKidneys produce urine and urine from kidney passes through the ureters into the urinary bladder and remains stored their until it is released through the urethra.\tUrine is produced to filter out waste products from the blood.\tNephrons are basic structural and functional unit of kidney.\tCluster of thin walled blood capillaries called glomerulus in the nephron filtrate the urine and each cluster is associated with cup shaped end of a tube called Bowman’s capsule.\tSubstances like glucose, amino acids, salts and a major amount of water is selectively reabsorbed from the initial filtrate as the urine flows along the tube.\tReabsorption depends on the amount of excess water in the body and dissolved waste to be excreted.\tThe urine from kidney enters the long tube called ureter.\tUreter connects the kidney with the urinary bladder and urine from the kidney is passed to urinary bladder and stored in the bladder.\tWhen the pressure in the expanded bladder leads to the urge to urinate, the urine is passed out through urethra. First kidney then bladder then urethra then out then toilet then gattar then patiala |
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