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) Both A and R are true and R is the correct explanation of A.

(b) Both A and R are true but R is not correct explanation of A

(c) A is true but R is false

(d) A and R are false

Answer 1

The correct option is (d) A and R are false.

Explanation:

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 possess 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.