Why is passive transport alone inadequate for the production of urine that is high in nitrogenous wastes? (A) Osmosis cannot target specific solutes - HSC - SSCE Biology - Question 9 - 2016 - Paper 1

Passive transport includes processes like diffusion and osmosis, which rely on the natural movement of substances from areas of high concentration to areas of low concentration. In contrast, the production of urine that is high in nitrogenous wastes necessitates the movement of certain solutes against their concentration gradients. This is essential to concentrate waste materials effectively in the urine, thus eliminating them from the body. Without the ability to move solutes against a gradient, the kidneys would be unable to efficiently filter and excrete nitrogenous wastes.