he kidneys of terrestrial mammals conserve water in the body by concentrating urine. The osmolarity of human blood is 300 mOsm/L, but human urine is generally about 1200 mOsm/L. The loop of Henle and the collecting duct are instrumental in maintaining osmotic gradients that make the concentration of urine possible.

Complete the diagram below using the following steps:

Place the pink labels, which indicate interstitial fluid osmolarity in mOsm/L, onto the correct pink targets. (Note that the numbers inside the nephron and collecting duct indicate the osmolarity of the filtrate at those different points.)
Place a red arrow to indicate active transport or a purple arrow to indicate passive transport onto the remaining targets. Do H2O, NaCl, and urea experience active transport, passive transport, or both? Keep in mind that the nephron's epithelium exhibits varying permeability to water and solutes along its length.

Labels can be used once,