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Question

Difficulty: MediumVertebrates: Homoiothermic Classes (Aves and Mammalia)

Which of the following nitrogenous waste products is excreted by birds (Aves) to conserve water and minimize body weight for flight, distinguishing them from mammals (Mammalia) which excrete urea?

  1. Uric acidAnswer
  2. B
    Ammonia
  3. C
    Urea
  4. D
    Amino acids

Answer

Uric acid is excreted by birds to conserve water and minimize body weight for flight.
Birds (Aves) are uricotelic organisms. They process nitrogenous waste into uric acid, a non-toxic compound that precipitates out of solution. This enables almost complete reabsorption of water in the cloaca, allowing waste to be eliminated as a light, semi-solid white paste, which significantly reduces the body weight required for flight.

Step-by-Step Solution

1
Identify the metabolic waste requirement for birds (Aves) adapting to flight.
Flight requires minimizing body weight and efficiently storing or conserving water.
Water is heavy to carry in large quantities during powered flight.
2
Compare nitrogenous waste forms between homoiothermic classes.
Mammals excrete water-soluble urea (ureotelic), whereas birds excrete non-toxic, insoluble uric acid (uricotelic) as a semi-solid paste.
Uric acid crystallization allows maximum water reabsorption in the cloaca, reducing weight.

Key Concept

Excretory adaptations in homoiothermic vertebrates (Aves vs. Mammalia)
Estimated Time:1m 0s
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Topics

Vertebrates: Homoiothermic Classes (Aves and Mammalia)

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