AP BIOLOGY

Detailed explanation-1: -Most nitrogenous waste in marine fishes appears to be secreted by the gills as ammonia. Marine fishes can excrete salt by clusters of special cells (chloride cells) in the gills.

Detailed explanation-2: -Urea and uric acid are the most common nitrogenous waste products in terrestrial animals; freshwater fish excrete ammonia and marine fish excrete both urea and trimethylamine oxide.

Detailed explanation-3: -Fishes in water excrete ammonia as the major nitrogenous waste through gills, but gills of air-breathing fishes are modified for air-breathing or largely replaced by air-breathing organs. Notably, fishes emerged from water can no longer excrete ammonia effectively because of a lack of water to flush the gills.

Detailed explanation-4: -Ammonia is the excretory waste in fishes. It is easily soluble and hence, is excreted by simple diffusion process across body surface or through their gills.

Detailed explanation-5: -Generally, aquatic animals excrete mostly ammonia, whereas terrestrial animals excrete either urea or uric acid. Ammonia, urea and uric acid are transported across cell membranes by different mechanisms corresponding to their different chemical properties in solution.