Which structure collects waste materials to form urine?

The nephron is the fundamental functional unit of the kidney, responsible for the process of filtering blood and forming urine. It comprises several key components, with the Bowman's capsule being one of them, where the initial filtration of blood occurs.

Within the nephron, the filtration process begins when blood enters through the glomerulus, encased by Bowman's capsule. This is where waste materials, as well as water and ions, are filtered from the blood. The filtered fluid, which contains waste products such as urea, then travels through the nephron's tubules, where further processing occurs—reabsorbing necessary substances back into the bloodstream and concentrating the waste to form urine.

Thus, while other options mention structures or substances involved in the urinary system, none encapsulate the entire process of collecting waste and forming urine like the nephron does. The renal artery is involved in supplying blood to the kidneys, and urea is merely a waste product stemming from protein metabolism, not a structure. Hence, the nephron's role as the comprehensive unit for waste collection and urine formation makes it the correct answer.