GENERAL HISTOLOGY

Detailed explanation-1: -Birds, reptiles, and most terrestrial arthropods convert toxic ammonia to uric acid or the closely related compound guanine (guano) instead of urea.

Detailed explanation-2: -Unlike mammals, birds don’t excrete the products of protein breakdown as soluble urea, but as uric acid. This is only marginally soluble, so is seen as a white paste. This comes from the kidney into the cloaca – the single orifice for excretion, urination, egg-laying and mating – where the faecal waste also empties.

Detailed explanation-3: -Birds excrete nitrogenous wastes as uric acid in the form of pellet or paste with minimum loss of water and are called uricotelic animals.

Detailed explanation-4: -Producing uric acid instead of urea is advantageous because it is less toxic and reduces water loss and the subsequent need for water.

Detailed explanation-5: -Instead, birds convert their ammonia wastes to a compound called uric acid. It takes more energy to convert ammonia to uric acid than to urea. However, the cost is worth it for birds because uric acid is non-toxic and also does not dissolve in water.