Biology - Excretory Products and their Elimination Question with Solution | TestHub

The given figure illustrates the counter-current mechanism in the nephron and vasa recta, which is responsible for maintaining an osmolarity gradient in the medullary interstitium.

The osmolarity of the interstitial fluid steadily increases from the cortex towards the inner medulla.

In the cortex (region A), the osmolarity is approximately $300$ $m{\text{O}}_{smol}$ L${}^{-1}$.

As we move deeper into the outer medulla (region B), the osmolarity increases to about $600$ $m{\text{O}}_{smol}$ L${}^{-1}$.

Further down in the inner medulla (region C), it reaches around $900$ $m{\text{O}}_{smol}$ L${}^{-1}$.

At the deepest part of the inner medulla (region D), near the tip of the loop of Henle, the osmolarity is at its maximum, which is $1200$ $m{\text{O}}_{smol}$ L${}^{-1}$.

Therefore, the correct identification is A - $300$ $m{\text{O}}_{smol}$ L${}^{-1}$, B - $600$ $m{\text{O}}_{smol}$ L${}^{-1}$, C - $900$ $m{\text{O}}_{smol}$ L${}^{-1}$, and D - $1200$ $m{\text{O}}_{smol}$ L${}^{-1}$.

Answer: A - $300$ $m{\text{O}}_{smol}$ L${}^{-1}$, B - $600$ $m{\text{O}}_{smol}$ L${}^{-1}$, C - $900$ $m{\text{O}}_{smol}$ L${}^{-1}$, D - $1200$ $m{\text{O}}_{smol}$ L${}^{-1}$