Metabolism and Excretion (pg 7)
Organisms rely on complex chemical reactionsto provide energy for responsiveness, growth, reproduction, andmovement. They must also synthesize complex chemicals, such as proteins.The term metabolism refers to all the chemical operations underway in the body: Catabolism is the breakdown of complex molecules intosimple ones, and anabolism is the synthesis of complex molecules fromsimple ones. Normal metabolic operations require the absorption of materialsfrom the environment. To generate energy efficiently, most cellsrequire various nutrients, as well as oxygen, an atmospheric gas. The term respiration refers to the absorption, transport, and use of oxygenby cells. Metabolic operations often generate unneeded or potentiallyharmful waste products that must be removed through the process of excretion.