A Level Biology Practice Exam 2025 – All-in-One Study Guide to Excel in Your A Levels!

The urinary system's primary function is to filter blood and eliminate waste products through urine. The kidneys play a crucial role in this process by filtering out toxins, excess salts, and water from the bloodstream, thereby regulating many aspects of homeostasis, such as fluid balance and electrolyte levels.

The bladder is equally important, as it serves as a storage organ for urine until it is expelled from the body. The coordinated function of both the kidneys and the bladder ensures that waste is efficiently removed and that the body's internal environment is kept stable.

In contrast, the heart and lungs are part of the cardiovascular and respiratory systems, which focus on circulation and gas exchange. The pancreas and liver are involved in digestion and metabolism, while the brain and spinal cord are central to the nervous system and control various bodily functions, but do not directly participate in waste elimination. Thus, the kidneys and bladder are the correct organs primarily involved in the urinary system.