Question

Statement I : Ammonia is highly toxic and needs more water for elimination and therefore excretion of ammonia is more common in aquatic animals.
Statement II : Urea is synthesised in kidneys.
Identify the correct option from the following

• A. Both statements I and II are true.
• B. Both statements I and II are false.
• C. Statement I is true, but statement II is false.
• D. Statement I is false, but statement II is true.

Hint:

Key facts about nitrogenous wastes: \textbf{Ammonia:} Most toxic, requires most water, common in aquatic animals (ammonotelic). \textbf{Urea:} Less toxic than ammonia, requires moderate water, synthesized in the \textbf{liver} (mammals, amphibians - ureotelic), excreted by kidneys. \textbf{Uric acid:} Least toxic, requires least water, common in birds, reptiles, insects (uricotelic).

Answer 1

The Correct Option is C

Step 1: Analyze Statement I)
Statement I says: "Ammonia is highly toxic and needs more water for elimination and therefore excretion of ammonia is more common in aquatic animals." Ammonia (NH\textsubscript{3}) is indeed the most toxic of the nitrogenous wastes (ammonia, urea, uric acid).
Due to its high toxicity, it requires a large amount of water for its elimination.
Aquatic animals (like most fish and aquatic invertebrates) have constant access to water, making ammonotelic excretion (excreting ammonia directly) an efficient strategy for them, as they can readily dilute and flush out the toxic ammonia. Therefore, Statement I is True. Step 2: Analyze Statement II)
Statement II says: "Urea is synthesised in kidneys."
Urea is the primary nitrogenous waste product in mammals, including humans.
However, urea is synthesized in the liver through the urea cycle (ornithine cycle), not in the kidneys.
The kidneys are responsible for filtering the urea from the blood and excreting it in urine. They do not synthesize urea. Therefore, Statement II is False. Step 3: Identify the correct option
Based on the analysis:
Statement I is True.
Statement II is False.
This matches option (3): Statement I is true, but statement II is false.