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, which includes processes like osmosis and diffusion, relies on the movement of substances down their concentration gradient. This means that solutes can only move from areas of higher concentration to areas of lower concentration. In the case of urine production, particularly when eliminating nitrogenous wastes, it is necessary to actively transport solutes against their concentration gradients to maintain the necessary concentrations and thus, enhance the elimination of waste. Therefore, passive transport alone is insufficient for this process.