The correct option is Lizards — Uric acid
Explanation
Animals are classified into three categories based on the primary nitrogenous waste they excrete: Ammonotelic (Ammonia), Ureotelic (Urea), and Uricotelic (Uric acid). The form of nitrogenous waste is an evolutionary adaptation primarily determined by the availability of water in the organism's habitat.
Analysis of Options:
- (a) Fishes - Urea: This is generally Incorrect. Most fishes (specifically bony fishes) are ammonotelic and excrete ammonia. Ammonia is highly toxic and readily soluble, requiring large volumes of water for excretion, which is feasible for aquatic animals. (Marine cartilaginous fishes like sharks are ureotelic, but the standard classification contrasts aquatic bony fishes with terrestrial groups).
- (b) Birds - Ammonia: This is Incorrect. Birds are uricotelic. To conserve water and reduce body mass for flight, they excrete nitrogenous waste as uric acid in the form of a semi-solid paste or pellet.
- (c) Humans - Uric acid: This is Incorrect. Humans are mammals and are ureotelic. The liver converts toxic ammonia into urea, which is less toxic and is excreted via the kidneys. While humans produce small amounts of uric acid from nucleic acid breakdown, urea is the primary excretory product.
- (d) Lizards - Uric acid: This is Correct. Lizards are reptiles, which are uricotelic. Like birds and land snails, reptiles excrete uric acid to minimize water loss, an essential adaptation for terrestrial survival.
Key Takeaway:
Ammonia is the most toxic waste requiring maximum water (Bony fishes). Urea is moderately toxic requiring moderate water (Mammals). Uric acid is the least toxic requiring minimum water (Reptiles, Birds, Insects).