Biology (0610) Excretion in Humans Revision Note

This document explains excretion in humans for CAIE IGCSE Biology, focusing on the removal of waste products of metabolism and substances in excess. Excretion is defined as the elimination of toxic materials such as carbon dioxide (lungs), urea, and excess water and salts (kidneys). The liver plays a vital role in assimilation and detoxification. It converts amino acids into proteins, carries out deamination to remove nitrogen from amino acids and form urea, and breaks down alcohol, drugs, and hormones. The kidneys maintain homeostasis by removing urea and excess water while reabsorbing glucose and essential salts. Their structure includes the cortex, medulla, ureter, bladder, urethra, renal artery, and renal vein. The nephron is explained step by step: (1) ultrafiltration in the glomerulus pushes water, salts, glucose, and urea into Bowman’s capsule while retaining large proteins and blood cells; (2) selective reabsorption of glucose, salts, and most water into the blood by active transport; (3) the loop of Henlé reabsorbs water via osmosis; and (4) the collecting duct directs remaining waste into urine. This guide highlights the importance of excretion for maintaining chemical balance and removing toxins in humans.