Organisms produce various waste by-products that require excretion to maintain internal balance. In animals, nitrogenous wastes like urea and ammonia result from protein metabolism and are eliminated through urine. Carbon dioxide, a by-product of cellular respiration, is expelled through respiration in both animals and plants. Plants excrete oxygen as a by-product of photosynthesis. In animals, excess ions (e.g., sodium, potassium) and metabolic by-products like bilirubin and creatinine also require excretion. Additionally, in plants, metabolic wastes such as organic acids may be released through processes like guttation. Efficient excretion of these by-products is vital for organismal health.