Question

Given alongside is a highly simplified diagram of the human kidney cut open longitudinally. Answer the questions that follow: [5 MARKS]
(a) Define excretion.
(b) Name the functional units of kidneys.
(c) Why does the cortex of the kidney show a dotted appearance?
(d) Mention two functions of the kidney.
(e) Write two differences in the composition of the blood flowing through the blood vessels, 'A' and 'B'.

Answer 1

Each Part: 1 Mark

(a) The process of removal of harmful and unwanted waste products (mainly nitrogenous) from the body, formed during various chemical reactions taking place in its living cells, is called excretion.

(b) The kidneys are composed of a vast number of minute tubules called nephrons or uriniferous tubules. These are the structural as well as functional units of kidney.

(c) These are nearly two million microscopic nephrons in two kidneys, Therefore, the cortex of kidney shows a dotted appearance.

(d) Functions of the kidney.
(i) Excretion - Removes nitrogenous metabolic wastes, excess salts, vitamins, bile pigments and excess water.
(ii) Osmoregulation - Regulates the osmotic pressure of the blood.

(e) Vessel 'A' is Renal Vein containing de deoxygenated cleaned blood free of toxic substances. Vessel 'B' is Renal Artery containing oxygenated dirty blood containing toxic nitrogenous wastes.

Renal Artery	Renal Vein
1. Blood is rich in urea.	1. Blood is nearly free of urea.
2. Blood has more salts of N$a^{+}$, $k^{+}$, N$H_4$	2. Blood has less or no salts of N$a^{+}$, $k^{+}$, N$H_4$
3. Blood is rich in oxygen.	3. Blood is rich in carbon dioxide.