Igcse Model Questions Vol1 2018 Biology Question 6

A 25‑year‑old male is investigated for dehydration after completing a marathon. The following renal data are obtained: - Glomerular filtration rate (GFR) = 120 mL min⁻¹. - In the proximal convoluted tubule, 65 % of the filtered Na⁺ and water are re‑absorbed. - In the loop of Henle, an additional 15 % of the filtered water is re‑absorbed, while Na⁺ re‑absorption is negligible. - In the distal convoluted tubule and collecting duct, under the influence of antidiuretic hormone (ADH), 80 % of the remaining water is re‑absorbed, while 5 % of the remaining Na⁺ is re‑absorbed. Assume that the filtered load of water equals the GFR (i.e., 120 mL min⁻¹) and that Na⁺ concentration in the filtrate is constant throughout the nephron.