An investigation was carried out comparing the metabolic energy costs and water requirements of excreting three different nitrogenous waste products (Waste I, Waste II, and Waste III) in vertebrates adapted to different habitats.
The graph below shows the relative water required for excretion and the metabolic energy cost of synthesis per nitrogen atom for each waste product.
The following statements relate to the adaptation of these excretory strategies:
- Waste I is ammonia; because of its high toxicity, mammals continuously convert it into urea within the kidneys before excretion.
- Waste II is urea; its excretion represents a physiological compromise between water conservation and the metabolic energy required for its synthesis.
- Waste III is uric acid; its extremely low solubility allows desert reptiles and birds to excrete it as a semi-solid paste, minimizing water loss at the expense of a high ATP requirement.
Which of the statements correctly describe these excretory adaptations?
1, 2 and 3
Only 1 and 2
Only 2 and 3
Only 2