Cells function similarly to factories in that both take up raw materials and use energy to produce waste and finished products. In the case of the cell, the finished products are proteins that can be used in building and operating the body.
In addition to the functional similarities between them, cells also resemble factories structurally and communally. The cell's outer plasma membrane is analogous to the walls of a factory, and its interior arrangement of organelles is approximately similar to the interior partitions that separate a factory's repair shop and painting room. The interior partition analogy breaks down, however, as most cells allow their constituent chemicals to mix freely, which is like a factory in which machinists and line workers occupy the same work spaces as the custodial staff and management.
Cells are also similar to factories in that they are individual units of production and consumption within the context of a much larger economy. Just as factories are isolated sites of economic activity that are connected to other factories and their markets in the larger community, cells are grouped into tissue types and specialized organs. Organs are, in turn, organized into systems within the body. In each case, small units work together to make a greater whole function smoothly.