Question

The mechanism of urine formation in nephrons involves.
A) Ultrafiltration
B) Secretion
C) Diffusion
D) Osmosis

Answer 1

Urine is the liquid by- product secreted by the kidney. The main purpose is to remove waste like urea, uric acid and excess of water from blood.

Complete answer:
Let us analyse the options to find the correct answer.

Option A: Ultrafiltration: The glomerular blood is filtered through the minute pores called filtration slits present in the wall of Bowman's capsule. The filtrate is collected by Bowman's capsule and passed to the proximal convoluted tubule. This phenomenon of filtration of glomerular blood through the filtration slits is called glomerular filtration. It is also called as ultrafiltration because relatively larger molecules like proteins cannot pass through filtration slits. Hence the mechanism of urine formation in nephrons involves 'Ultrafiltration'. Therefore, this is the correct option.
Option B: Secretion : Cells of Proximal convoluted tubules and Distal convoluted tubules [ Part of nephron]maintain ionic (Na-K balance) and acid-base balance (pH) of body fluids by selective secretion of $H^+$, $K^+$ & $NH_3$ into Collecting duct maintain pH and ionic balance of blood by the secretion of H+ and K+ ions. It makes urine concentrated. Therefore, this is the incorrect option.
Option C: Diffusion: The movement of ions or molecules or gases from a region of higher concentration to a region of lower concentration. It will not help in the process of urine formation. Therefore, this is the incorrect option.
Option D: Osmosis: The movement of solvent molecules or water molecules through a semipermeable membrane from a dilute solution to a more concentrated solution. It will not help in the process of urine formation. Therefore, this is the incorrect option.

Thus, the correct answer is option (A) Ultrafiltration.

Note: Uremia is a disease which is caused by accumulation of urea in blood which may lead to kidney failure. When kidneys are not able to perform their function, dialysis is recommended by the doctor.