The evolution of oxygen-producing (“oxygenic”) photosynthesis was a turning point in Earth’s history. The atmosphere started to fill with oxygen, and then the first chloroplasts arose.
Aerobic respiration continues in specialized organelles of the eukaryotic cell, the mitochondria. These are the descendants of ancient bacteria who evolved to use oxygen to completely oxidize their fuel compounds.
We need energy to do work, and we get that energy from chemicals. In the same way that a hydrogen-powered car uses a fuel cell to get energy from hydrogen, …