Question

Select the INCORRECT statement related to tubular secretion.

• A. Tubular secretion is the only mode of excretion in marine bony fishes and desert amphibians.
• B. Tubular secretion helps in changing the pH of urine from acidic to alkaline.
• C. During tubular secretion, cells of distal convoluted tubule actively absorb creatinine, \(\text{K}^{+}\), \(\text{H}^{+}\), etc. from peritubular capillaries.
• D. During tubular secretion, cells of distal convoluted tubule secrete creatinine, \(\text{K}^{+}\), \(\text{H}^{+}\) etc. from peritubular capillaries into lumen of DCT and CT.

Hint:

Tubular secretion of hydrogen ions makes urine slightly acidic, so it does not change urine from acidic to alkaline.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept
In tubular secretion, cells of the DCT and collecting tubule take wastes from peritubular capillaries and release them into the lumen.

Step 2: Check the statements
Statements about taking up and secreting creatinine, potassium and hydrogen ions are true.
In marine bony fishes and desert amphibians, glomeruli are reduced or absent, so excretion depends on tubular secretion alone: true.

Step 3: pH effect
Secretion of hydrogen ions into the filtrate lowers its pH, so the urine becomes slightly acidic and blood pH stays near 7.4.
The statement of change from acidic to alkaline is wrong.

Step 4: Conclusion
Option (B) is the incorrect statement.

Final Answer:
The statement about changing urine from acidic to alkaline is incorrect. \[ \boxed{\text{(B) }\text{Tubular secretion helps in changing the pH of urine from acidic to alkaline.}} \]