Until the End of Time: Mind, Matter, and Our Search for Meaning in an Evolving Universe

by Brian Greene

In living cells—let’s focus on animals to be definite—similar redox reactions take place but, importantly, the electrons stripped from atoms that you ingested at breakfast are not transferred directly to oxygen. If they were, the energy released would create something akin to a cellular fire, an outcome life has learned the benefit of avoiding. Instead, electrons donated by food pass through a series of intermediate redox reactions, rest stops on a trek that ultimately ends with oxygen but that allows smaller amounts of energy to be released at each step. Like a ball in the bleachers cascading down a stadium’s steps, electrons jump from one molecular receptor to another, with each receptor more electron crazed than the previous, ensuring that each jump results in the release of energy. Oxygen, the most electron-crazed receptor of all, waits for the electron at the bottom of the stairs, and when it finally arrives, the oxygen hugs the electron tight, squeezing out the marginal energy it can still provide, thus concluding the energy extraction process. The process for plants is largely the same. The main difference is the source of the electrons. For animals, they come from food. For plants, they come from water. Sunlight striking chlorophyll in the green leaves of plants strips electrons from water molecules, pumps up their energy, and sets them off on a similar energy-extracting redox cascade. And so the energy supporting all the actions of all living things can be traced ...