Answer: Urea.
- A Uric acid
- B Urea
- C Ammonia
- D CO<sub>2</sub>
Correct answer: B. Urea
Explanation: Urea is the main nitrogenous waste in humans, formed in the liver from ammonia (produced by deamination of amino acids).
Filtrate flows through four functionally distinct stages of the nephron: Bowman's capsule filters blood, the PCT reabsorbs most useful substances unconditionally, the Loop of Henle builds a concentration gradient via counter-current exchange, the DCT secretes selected substances, and the collecting duct performs the final ADH-controlled water reabsorption.
Concept context
Nitrogenous waste, kidney structure, urine formation in the nephron, and hormonal regulation of excretion.
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