The elimination by an organism of waste products that  result from metabolic processes. In plants, waste is minimal and is eliminated  primarily by diffusion to the outside environment. Animals have specific organs  of excretion. In vertebrates, the kidney filters blood, conserving water and  producing urea and other waste products in the form of urine. The urine is then  passed through the ureters to the bladder and discharged through the urethra.  The skin and lungs, which eliminate carbon dioxide, are also excretory  organs.
Thursday, August 20, 2009
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