An essential yet less captivating system that supports both buildings and humans is waste management. The urinary system and large intestine are responsible for eliminating liquid and solid waste from the body. In buildings, plumbing systems manage liquid waste by directing grey and black water to the public sewer system. Meanwhile, trash chutes vertically move and consolidate trash to the ground floor for bulk disposal.
Regarding power supply, most buildings connect to the electrical grid. However, when the grid fails, a building must either support itself or remain offline for a period of time. Mitochondria is analagous to on-site generators, as they generate internal power to sustain the necessary functions of either the cell or the building.
A more abstract analogy compares windows to eyes. Both allow us to see the outside world while providing a limited layer of protection compared to their opaque counterparts.