What is the kidney's main role?

• A. To store minerals for the body.
• B. To filter blood, produce urine, and maintain water and ion balance.
• C. To pump blood through the body.
• D. To produce hormones regulating metabolism.

Answer: (B)

The kidney’s job is to keep the body in balance by filtering the blood, forming urine, and controlling how much water and which ions are kept or lost. Inside the kidney, tiny filtering units called nephrons remove waste and excess substances from the blood to make urine. As this filtrate moves along the tubules, useful substances such as water, salts, and nutrients are reabsorbed back into the blood, while wastes like urea are left to be excreted. This process lets the body maintain proper fluid levels and electrolyte balance, which are essential for nerves, muscles, and overall cell function. It also helps keep the blood’s pH in the right range.

Storing minerals is not the kidney’s main function—the minerals are largely stored in bones and tissues. Pumping blood is the heart’s function. Producing hormones that regulate metabolism is mainly associated with other organs, though the kidneys do release hormones like erythropoietin and renin as part of maintaining blood conditions, the central role here is filtering blood, forming urine, and balancing water and ions.