AP BIOLOGY

Detailed explanation-1: -This part of the nephron is called the loop of Henle. Its main function is to reabsorb water and sodium chloride from the filtrate. This conserves water for the organism, producing highly concentrated urine.

Detailed explanation-2: -In summary, the loop of Henle is surrounded by tissue fluid which has a high concentration of ions in it. This causes water to move out of the descending limb by osmosis. This produces a more concentrated filtrate because of this, ions move out of the loop in the thin ascending limb.

Detailed explanation-3: -Water is readily reabsorbed from the descending limb by osmosis. Also, the medullary interstitium is highly concentrated (because of the activity of the ascending limb), leading to a strong osmotic gradient from the descending limb to the medulla.

Detailed explanation-4: -The descending loop of Henle is highly permeable to water due to the presence of aquaporin proteins. Aquaporins are protein channels that facilitate the passive transport of water across it.

Detailed explanation-5: -The descending limb is highly permeable to water, with reabsorption occurring passively via aquaporin-1 (AQP1) channels. Small amounts of urea, sodium (Na+) and other ions are also reabsorbed.