The removal of toxic, waste metabolic products from the body is known as excretion. All plants and animals produce harmful substances due to a number of metabolic activities occurring in their bodies. Carbon dioxide produced during respiration is removed by lungs.
Plants have no special organs for removal of wastes. The waste products of respiration and photosynthesis are used as raw materials for each other. Oxygen gas produced as a by-product of photosynthesis is used up during respiration and carbon dioxide produced during respiration is used up during photosynthesis.
The human body has various organs for the purpose of excretion such as lungs, skin, large intestine and urinary system. Lungs excrete carbon dioxide and water vapor formed during the process of respiration. Skin removes urea, salts and excess water as sweat produced by sweat glands present in the skin. Sweat is removed through tiny pores in the skin.