Question

Assertion : Secreting hypotonic urine is effective in reducing urinary loss of water.
Reason : Hypotonic urine is more concentrated and higher in osmotic pressure than the blood.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (D)

Both the assertion and reason are false. When there is a threat of excessive water loss from the body of the animal, then the urine excreted needs to be hypertonic and not hypotonic because excessive water loss from the body posses the threat of a rise in osmoconcentration of the blood. Since hypertonic urine is more concentrated and higher in osmotic pressure than the blood, therefore it helps in reducing the loss of water with urine. Mammals and birds can excrete hypertonic urine which is more concentrated than their blood. For this, an isotonic glomerular filtrate is first filtered into the Bowman’s capsules of nephrons in kidneys. The tubules of nephrons then reabsorb a large volume of water from the glomerular filtrate not accompanied by the reabsorption of proportionate amounts of solutes. This leaves the urine more concentrated than the blood which is very effective in reducing the urinary loss of water.