Which adaptation is shown by desert organisms?

Salmon have gills that are more permeable to water than to salts. Salmon hatch in fresh water streams and then migrate to the ocean. Once they reach the ocean,you would expect the rate of uptake of water into their body through the gills to:

If the $Loop$ $of$ $Henle$ is absent from the mammalian nephron,which of the following is likely to occur?

The shape of vasa recta is

$A$: The final reabsorption of water from urine into blood occurs through the collecting duct of a mammalian nephron,resulting in the production of hyperosmotic urine.
$R$: The loop of Henle is responsible for the formation of a sodium gradient across the depth of the medullary interstitium of a mammalian kidney.

Urine is concentrated in which part of the nephron?