Grade 8 Biology Practice Test

The kidneys are the organs responsible for filtering blood in the human body. They play a critical role in maintaining homeostasis by regulating the balance of water, salts, and minerals, while also removing waste products and toxins from the blood. Blood enters the kidneys through the renal arteries, where it passes through tiny filtering units called nephrons. These nephrons extract waste and excess substances from the blood, forming urine, which is then excreted from the body.

The liver, while it filters substances from the blood, primarily focuses on processing nutrients, detoxifying harmful substances, and producing bile to aid in digestion, rather than filtering out the blood in the same way that the kidneys do. The heart is primarily responsible for pumping blood throughout the body, not filtering it. The lungs facilitate gas exchange, removing carbon dioxide and bringing in oxygen, but they do not filter blood in the same sense as the kidneys. Thus, the kidneys are specifically designed for the function of blood filtration, making them the correct answer.