Microorganism A is good at producing (say) insulin, but needs oxygen to do it. Microorganism B is good at ferrying oxygen around. Microorganism C is good at extracting oxygen from the air and attaching it to B.

Each of these cells has specialized tasks which they perform as part of the contract of getting to survive longer in the superorganism. Each has 'promises' (functions) to fulfill, and other organisms provide for their needs. The contract is set up on evolutionary timescales, rather than human timescales, but your requirements are met...