Plants do not excrete ammonia, urea and uric acid because:

Explanation

Otherwise, overwhelmingly, nitrogenous waste metabolites constitute the excretory products. Primarily, in the catabolism of animo acids the amino group (---NH2) is released (deamination) or transferred to another molecule for removal or reuse. Amino group not reused for recycling of amino acids is essentially dissolved in water and excreted to avoid toxic rise in the plasma. Elevated levels of these wastes can cause convulsions, coma and eventually death. Mostly excess nitrogen is excreted by animals as ammonia, urea or uric acid (Fig. 15.5). Lower quantities of nitrogen are excreted in the form of other compounds such as creatinine, creatine, or dimethylamine oxide and in very small quantities as amino acids, purines, and pyrimidines. Metabolism of purine and pyrimidine bases produces significant amount of nitrogenous wastes of hypoxanthine, xanthine, uric acid, allantoin, urea and ammonia.