CBSE Class 10 Science 2020 · Paper 31/2/1 · Question 27

(a) The basic filtering unit of the kidney is the nephron. Structure: each nephron has a cup-shaped Bowman’s capsule at its upper end, which holds a cluster of thin-walled blood capillaries called the glomerulus; blood enters the glomerulus through a branch of the renal artery and leaves through another arteriole. Bowman’s capsule leads into a long coiled tubule, surrounded by blood capillaries, which opens into a collecting duct. Function: blood is filtered in the glomerulus and the filtrate (water, glucose, amino acids, salts and urea) collects in Bowman’s capsule. As the filtrate passes along the tubule, useful substances such as glucose, amino acids, salts and a major amount of water are selectively reabsorbed into the surrounding capillaries. The remaining fluid, urine, passes into the collecting duct and on to the ureter. (b) The reabsorption of water depends on (i) the amount of excess water in the body and (ii) the amount of dissolved waste (such as urea) to be excreted.