Final answer:
The most functional portion of the kidney is the nephron, responsible for filtering blood, reabsorbing needed substances, and excreting waste as urine. The correct option is C.
Step-by-step explanation:
The most functional portion of the kidney is c. Nephron. The nephron is the functional unit of the kidney and each kidney contains over one million nephrons. A nephron consists of three parts: the renal corpuscle, the renal tubule, and the associated capillary network.
The renal corpuscle performs the initial filtration of the blood through the glomerulus, and the renal tubule processes the filtrate, ultimately leading to the production of urine.
Nephrons are predominantly located in the renal cortex and play a critical role in the kidneys' ability to maintain homeostasis in the body by regulating the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine.