A cell generates waste. Carbon dioxide and urea, the by products of energy production are expelled and disposed of elsewhere. Many components of the cell eventually wear out and need to be broken down and the parts recycled.
This activity takes place inside the cell in specialized compartments called lysosomes. A mitochondrian, for example that has passed its sell-by date, will be engulfed, disassembled and reused by the cell. The beauty of the cell is that most of its waste is recycled.
Lysosomes are fluid-filled ‘bags’ of membrane, which contain a cocktail of molecules for breaking down complex molecules and providing the cell with the simpler nutrients it requires. They also have a role in defence against infection as they are used to digest and remove any infiltrating infection.
All manufacturing creates waste product, which needs to be disposed of. A city generates waste. Some waste is transported away, for example, to land-fill sites, whereas other waste is disposed of inside the city. Nowadays, environmental and economic issues are important, therefore, as much waste as possible is broken down and recycled.
Examples in a city of waste recycling, are water recycling and a car breakers yard.