excretion
In biology, the removal of the waste products of metabolism from living organisms. In plants and simple animals, waste products are removed by diffusion. Plants, for example, excrete O2, a product of photosynthesis. In mammals, waste products are removed by specialized excretory organs, principally the kidneys, which excrete urea. Water and metabolic wastes are also excreted in the faeces and, in humans, through the sweat glands in the skin; carbon dioxide and water are removed via the lungs. The liver excretes bile pigments.
