Answer:
a. Proximal convoluted tubule is responsible for reabsorbing most part of the ultrafiltrate. This means that at this level, substances like glucose and amino-acids are reabsorbed almost completely throughout this tube. Other substances, like potassium and bicarbonate are also reabsorbed in a big percentage here.
Also depending on the organism needs to keep the water balance, sodium, chloride and water are reabsorbed partly.
b. If the glucose transport is exceeded in the PCT, glucose will pass to the filtrate. Given the fact that glucose is osmotically active, high concentrations of glucose not being reabsorbed will consequently 'drag' water along. This situation ends up in an increase urine volume.
When diabetes mellitus is not controlled, patients will experience high volume of urine. Meaning they feel the need to go to the toilet very often. Also there is presence of glucose in the urine, which is normally not there.
c. The nephron loop is designed so the urine can be concentrated, saving water. The TCP is connected to the descending limb of the nephron loop, which is very permeable to water but not to other solutes like ions and urea. Then the following ascending limb of the loop, is not permeable at all to water, but ions can be reabsorber, especially cations. Therefore in a non pathological situation. This mechanism enables the production of concentrated urine when needed to save water and more diluted urine if there was a need to excrete water.
