Metabolism and its waste
Not everything an organism takes in gets used. The waste left over has to be put out of the body.
Every organism takes materials from the environment and converts them into the useful energy it needs. Alongside that, it discharges back into the environment the materials it did not use and the waste it produced. Otherwise those materials would collect inside the body and create a toxic condition.
Metabolism and excretion
The sum of the building up and the breaking down that happens inside cells is called metabolism.
Removing from the body the waste produced during metabolic activity is excretion.
Extra knowledge
Anabolism
The process of synthesising complex compounds from simple substances within a living body. Energy is stored in it.
Catabolism
The process of releasing energy within a living body by breaking complex substances down into simple ones.
Metabolism
All the biochemical reactions occurring within a living body — that is, anabolic and catabolic activity taken together.
Photosynthesis is anabolic; respiration is catabolic. Both together are metabolism.