Biology STAAR (State of Texas Assessments of Academic Readiness) Practice Test

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Study for the Biology STAAR Test. Improve your skills with flashcards and multiple choice questions, each question is accompanied by hints and explanations. Prepare for success!

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

To filter waste from the blood
To transport nutrients throughout the body
To produce hormones for growth
To facilitate gas exchange in the lungs

The correct answer is: To filter waste from the blood

The kidneys play a critical role in the excretory system by filtering waste products from the blood. Their primary function is to remove toxins, excess salts, and urea, which is a byproduct of protein metabolism, from the bloodstream. This filtration process occurs in tiny structures within the kidneys called nephrons. As blood passes through the nephrons, waste products are separated and concentrated into urine, which is then excreted from the body. This essential function helps maintain homeostasis by regulating the body's fluid balance, electrolyte levels, and blood pressure. Transporting nutrients throughout the body refers to the role of the circulatory system rather than the kidneys. While the kidneys do have some hormonal functions, particularly in regulating blood pressure and red blood cell production through the release of erythropoietin, their main task is not hormone production. Facilitating gas exchange occurs specifically in the lungs, not the kidneys, as oxygen is absorbed into the blood and carbon dioxide is expelled. Thus, the kidneys' primary responsibility in the excretory system is indeed to filter waste from the blood.