CBSE Class 10 Answered

Alveoli are small balloon like structures present within the lungs to increase the surface area of lungs. Their walls contain an extensive network of blood-vessels. CO₂ brought by blood from rest of the body is released into the alveoli and oxygen in the alveolar air is taken up by blood in the alveolar blood vessels to be transported to all the cells in the body. Thus exchange of gases takes place here and the deoxygenated blood is oxygenated here.

Nephrons on the other are functional units of kidney. They are long, tubular structures, concerned with filtration of blood. They are surrounded by a rich capillary network. Different parts of nephron absorb water and useful substances from blood and remove the harmful substances into the filtrate, which finally forms the urine.

Thus alveoli are sites of exchange of gases and oxygenation of deoxygenated blood whereas nephrons are sites of filtration of blood where water and useful substances are reabsorbed and nitrogenous wastes excreted.