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Question 8 |
(a) (i) What is excretion? [2 marks]
(ii) List the excretory organs in humans and name one waste product excreted by each organ. [8 marks]
(b) How does the mammalian kidney function as an excretory organ? [8 marks]
(c) Name the excretory organs in:
(i) insects;
(ii) earthworms. [2 marks ] |
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Most candidates attempted this question. They were able to define excretion and list the excretory organs and products in humans. However, they could not explain how the mammalian kidney functions as an excretory organ. They could name the excretory organs in insects and earthworm but some spelt them wrongly.
The expected answers are:
8 (b) Functioning of kidney as excretory organ
Blood from the renal artery enters the bowman’s capsule; through the afferent arteriole; ultra filtration occurs in the Bowman’s capsule; high pressure in the glomerulus causes the filtration of small molecules/amino acids/ glucose/ minerals salts/ water/ urea; out of the blood plasma into the cavity of the capsule; the filtrate/glomerular filtrate passes through the nephron; where selective reabsorption of useful metabolites/glucose/amino acids take place;
in the descending/first/proximal convoluted/coiled tubule; the reabsorption of salts and water is regulated in the loop of Henle; and the ascending/second/distal convoluted tubule/large waste molecules like creatine secreted at loop of Henle; depending on blood concentration; the filtrate continues into the main collecting duct/tube; where further reabsorption of water and salt takes place; the remaining fluid in the duct becomes urine.
(c) Excretory organs inss
(i) Insects - Malpighian tubules;
(ii) Earthworm - Nephridia/Nephridium
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