Which is the respiratory unit of the lungs and the excretory unit of the kidneys?

The respiratory unit of the lungs are alveoli, and the excretory unit of the kidneys is the nephron.

The alveoli are the specialized air sacs (outpouching) of 200 µ   diameter. These are the structural and functional units of the respiratory system. These are the primary sites of the exchange of oxygen and carbon dioxide.

Each human kidney has 1, 000, 000 nephrons. Nephron helps the kidney to filter impurities from the blood from ultrafiltration. This process occurs when the blood pressure forces water and other small molecules through tiny gaps in the capillary walls. This substance without blood cells and large molecules in the bloodstream is ultrafiltrate. This travels through various loops of nephrons where the impurities are removed and collected in the bladder.