About 150 l of plasma filters into the renal tubules each day, but only 1-2 l of urine is formed. what happens to the rest of the plasma fluid?

The rest of the plasma fluid is reabsorbed into the blood stream. This comprises of the nutrients and water. The unwanted materials i. e. solutes, water etc do concentrate to form the urine and the other filtrated products are therefore reabsorbed.