The diagram below shows what happens during filtration in the glomerulus of a kidney. (f) Explain what happens to molecules in the filtrate before urine leaves the kidney.

The fluid in the renal capsule is a solution of glucose, salts and urea are dissolved in water. All the glucose, some of the water and some of the salts need to be kept in the blood. Useful substances from the fluid in the kidney tubule are reabsorbed and pass back into the blood in these capillaries. The remaining fluid continues on its way along the tubule. By the time it gets to the collecting duct, it is mostly water with urea and salts dissolved in it. It is called urine.