What is the primary function of the kidneys in the excretory system?

• A. To filter waste and excess substances from the blood
• B. To produce hormones only
• C. To absorb nutrients from food
• D. To regulate body temperature

Answer: (A)

The primary function of the kidneys in the excretory system is to filter waste and excess substances from the blood. This key role ensures that metabolic waste products, such as urea and creatinine, are effectively removed from the bloodstream, thus maintaining the body's internal environment in a state of homeostasis.

The kidneys also help to regulate the balance of electrolytes and fluids, contributing to overall fluid balance and blood pressure regulation. By filtering blood, they produce urine, which carries away the wastes and excess substances. This process is essential for preventing the buildup of toxic metabolites and for ensuring that the body's chemical composition remains stable.

In contrast, the other options are not primary functions of the kidneys. While they do produce hormones, this is not their main function; they do not absorb nutrients from food, as that role falls primarily to the digestive system; and regulating body temperature is managed by the skin and other mechanisms rather than being a direct function of the kidneys. Thus, the role of the kidneys in filtration and waste removal remains central to their importance in the excretory system.