Which organ contains about a million filtering units known as nephrons?

• A. Heart
• B. Liver
• C. Kidneys
• D. Lungs

Answer: (C)

The main idea is where the body’s blood filtration happens and what those filtering units are. Nephrons are the kidney’s microscopic filtering units, and there are about a million of them in each kidney. Their job is to filter waste and excess fluid from the bloodstream, reabsorb what the body still needs, and form urine that carrying away wastes. This process starts in the glomerulus, where blood is filtered, and continues through the tubules that reclaim water, salts, and nutrients while tweaking what’s secreted into the urine. That combination of filtration, reabsorption, and secretion keeps fluid balance and waste removal in check.

The other organs don’t house this vast network of filtering units. The heart’s role is to pump blood, the liver processes nutrients and detoxifies chemicals, and the lungs exchange gases. While they’re essential for overall function, the kidneys are the organs that contain the million nephrons responsible for filtering blood.