Explanation

Excretion removes metabolic waste products. Main excretory organs: kidneys (urea, water, salts in urine), lungs (carbon dioxide, water vapor), skin (small amounts of urea, salts in sweat), liver (produces urea from amino acid breakdown).

Kidneys filter blood through nephrons. Useful substances are reabsorbed; wastes form urine. Kidney failure requires dialysis (machine filtration) or transplant.

This differs from egestion (removing undigested food as feces). Excretion removes waste from metabolism; egestion removes waste that was never absorbed. Both are essential for health.