The graph shows the solute concentration of the tissue fluid in the medulla of a kidney at increasing distances from the cortex.
Describe how the solute concentration of the tissue fluid changes from the cortex to the tip of the medulla.
[1]
Explain how the ascending limb of the loop of Henle produces this gradient.
[3]
Explain how this gradient causes water to be reabsorbed from the collecting duct.
[2]