**Core Concept**
Proximal convoluted tubule (PCT) plays a crucial role in the reabsorption of various substances from the filtrate back into the bloodstream. Approximately 65-70% of water, 85% of glucose, and 100% of amino acids and bicarbonate ions are reabsorbed in the PCT.

**Why the Correct Answer is Right**
The PCT is highly efficient in reabsorbing glucose, amino acids, and bicarbonate ions through secondary active transport mechanisms. The sodium-glucose cotransporter 2 (SGLT2) is responsible for the reabsorption of glucose, while the sodium-potassium pump maintains the low intracellular sodium concentration required for this process. Additionally, the reabsorption of bicarbonate ions is facilitated by the carbonic anhydrase enzyme, which helps maintain acid-base balance in the body.

**Why Each Wrong Option is Incorrect**
**Option A:** The distal convoluted tubule (DCT) is involved in the regulation of calcium and magnesium reabsorption, but it is not the primary site for glucose, amino acid, or bicarbonate reabsorption.
**Option B:** The loop of Henle is responsible for the reabsorption of water, ions, and urea, but it is not the primary site for glucose, amino acid, or bicarbonate reabsorption. The descending limb of the loop of Henle is highly permeable to water, while the ascending limb is involved in the reabsorption of ions such as sodium, potassium, and chloride.
**Option C:** The collecting duct is involved in the regulation of water, acid-base balance, and electrolyte reabsorption, but it is not the primary site for glucose, amino acid, or bicarbonate reabsorption. The collecting duct is also responsible for the secretion of potassium ions.

**Clinical Pearl / High-Yield Fact**
The PCT is highly susceptible to damage in conditions such as acute tubular necrosis (ATN), which can lead to a significant loss of reabsorptive function and impaired kidney function.

**Correct Answer:** D. Proximal Convoluted Tubule