K.C.S.E Biology Q & A - MODEL 1995PP1QN17

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​Describe how excretion takes place in
(i) Mammalian Kidneys
(ii) Green plants

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KNEC ANSWERS

​(i) Mammalian Kidney

• Blood reaches the kidney from the renal/ renal artery  enters the kidney; then branches  into  capillaries/ glomeruli/ in the  Bowmna’s capsule, blood vessels  leaving the capsule/  efferent are those entering it/ afferent causing high pressure to develop  in the glomeruli. This forces the plasma/ causes ultra filtration into the capsule. The filtrate contains waste products (acc. One example) The filtrate moves  into the proximal/ first convolulated tubule; where selective  reabsorption of glucose  amino acids, some water  and vitamins  take  through the loop of  henle; excretory products/  urea, excess water and salts acc, one  example) pass  into the distal tubule, where the remaining  useful substance (acc. One example e.g salts and water) are reabsorbed; The filtrate  passes into  the collecting tubule; where  more reabsorption of water  takes place: Excess water, urea and salts (  all  three  must  appear)/Urine  are removed through  the ureter.

(ii) Green plants

• CO2 / O2 /H2O diffuse through the stomata lentils/ hydrathods  some  toxic wastes are converted  into non – toxic substances; these are  deposited in certain tissues of the plant/ stored  in ageing structures.  Resins/ tannins – are exuded though the  bark of  the stem; or lost during leaf fall.