Question

Urinary bladder is absent in
(a) Amphibians
(b) Mammals
(c) Lizards
(d) Aves

Answer 1

Hint: Urinary bladder is a pouch-like structure that stores the urine and allows urination in an infrequent and controlled manner. The urinary bladder is absent in feathered bipeds which are truly vertebrates and possess beak and also have a streamlined body.

Complete answer:
The urinary bladder is absent in Class Aves that comprises birds. They lack a urinary bladder because the waste product mostly contains uric acid that is, they are uricotelic and excrete the waste along with the feces. The absence of a urinary bladder also lightens up their body weight and helps in maintaining equilibrium while flying.

Additional Information: Ammonia, urea, and uric acid are the most common nitrogenous wastes excreted by the animals. Ammonia is the most toxic form and requires a large amount of water thus mostly excreted by the aquatic animals. Uric acid is the least toxic and requires less amount of water.
Reptiles, birds, land snails, and insects excrete nitrogenous waste in the form of uric acid. It is excreted in the form of a pellet or paste with a minimum loss of water and are called uricotelic animals. Excretion of uric acid is known as uricotelism.
Uricotelism is important in land vertebrates that lay eggs because if the embryo within the shelled egg had produced ammonia or urea as a waste product it would have accumulated to the toxic level. However, this problem is solved by being uricotelic, as uric acid is almost insoluble, gets precipitated, and remains with the shell only. This problem is not faced by eggs laying fishes or amphibians by having shell-less eggs (ammonia or urea can diffuse out) or mammals (as urea is carried away by the maternal blood at the placenta).
So, the correct answer is, “Aves.”

Note: -Other than birds, the urinary bladder is absent in some lizards, snakes, crocodiles as they excrete semisolid waste which contains uric acid. Thus, it is excreted with the feces.
-Ostrich is the only bird that has a urinary bladder.
-Hummingbird is ammonotelic i.e., it excretes ammonia as the waste product at low temperature and high-water intake whereas they are uricotelic in high temperature and low water intake. Thus, they are facultative ammonotelic.
 -Ureters directly join the cloaca, from which they excrete nitrogenous waste along with their feces.