Kidneys' Roles in Filtration and Waste Removal

Steps:

• Recall that kidneys filter blood to maintain homeostasis by removing waste products.
• Identify main functions: excretion of urea (from protein breakdown) and elimination of toxins like drugs or metabolic byproducts.
• Evaluate options against these functions: check for accurate waste removal without unrelated processes.
• Select the option matching both urea removal and toxin elimination.

Why B is correct:

• Kidneys act as filters in the nephrons, removing urea (nitrogenous waste) and toxins from blood plasma via glomerular filtration and tubular reabsorption/secretion, as defined in renal physiology.

Why the others are wrong:

• A: Kidneys regulate salt but primary functions focus on broader toxins, not just excess salt.
• C: Urea removal is correct, but glucose-to-glycogen conversion occurs in the liver, not kidneys.
• D: Glucose conversion is a liver function; kidneys detoxify but do not produce toxins.

Final answer: B