Paul Andersen introduces the concept of bioenergetics. He explains how living organisms utilize free energy in the Universe. He begins with a brief discussion of thermodynamics and Gibbs free energy. He then explains how reactions can be exergonic or endergonic. He also introduces the concepts of photosynthesis and cellular respiration.
This perspective escapes most mainstream academics because they don’t like to treat ambient / atmospheric or whatever other universal energy as “free.” Mainstream science always likes to put a “price tag” on anything that’s used as fuel.
Of course, we can treat ourselves from the perspective that we need to pay for energy in the form of food. We also need to pay for nutrients and water for our vegetable gardens. But let’s examine bioenergetics without those human controls and “price tags” for a moment. After all, there are organisms on this planet that have been around far longer than humans without worrying about a price tag: