Which organ excretes water and waste products from the body?

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

Answer: (B)

The kidneys are the body's main organ for excreting water and waste. They filter the blood to remove waste products like urea and excess salts, and they regulate fluid balance by deciding how much water to keep or eliminate as urine. In the nephron, filtration at the glomerulus is followed by selective reabsorption and secretion along the tubules, producing urine that reflects the body's hydration and electrolyte needs. Hormonal signals, especially antidiuretic hormone, influence how concentrated or dilute the urine becomes. The urine then travels through the ureters to the bladder and is excreted. While other organs contribute to elimination—lungs release carbon dioxide and water vapor, the skin expels sweat, and the liver processes and excretes certain wastes—the kidneys are the primary organ responsible for removing water and most waste products from the body.