-Excretion is the removal of wastes.
-Wastes from:
-Cellular respiration
-Digestion of Food
-Cellular activities.

-The skin is very important to the excretory system.
-Excretes excess:

What is urea?
-A common metabolic cellular waste product is ammonia.
-It can raise the pH of blood.
-The human body can combine ammonia and CO2 to make Urea.
-Urea is very soluble in water, making it an easy way to excrete excess nitrogen.