CBSE Class 10 Science 2020 · Paper 31/3/2 · Question 27

(a) Leaves help in excretion in these ways (any two): (1) oxygen produced in photosynthesis and carbon dioxide produced in respiration are given out through the stomata; (2) excess water is removed as water vapour by transpiration; (3) waste products stored in the vacuoles of leaf cells are removed when the old leaves fall off. (b) Structure: a nephron is the basic filtration unit of the kidney. It is a long, fine, coiled tubule whose one end forms a cup-shaped Bowman’s capsule around a cluster of thin-walled capillaries, the glomerulus (supplied by a branch of the renal artery); the tubule is surrounded by capillaries, and its other end opens into a collecting duct. Function: blood carrying nitrogenous wastes such as urea is filtered in the glomerulus, and the filtrate is collected in Bowman’s capsule. As the filtrate flows along the tubule, useful substances such as glucose, amino acids, salts and much of the water are selectively reabsorbed into the surrounding capillaries. The remaining fluid is urine, which passes into the collecting duct and then to the ureter.