Perhaps the most important chemical reactions on the planet take place inside a plant's chloroplasts. In this tiny green organelle, plants have the capacity to capture the energy in light and use that energy to convert CO2 gas into building blocks used to produce all four categories of biological molecules—lipids, carbohydrates, proteins and nucleic acids. Animals could not survive if plants did not exist. Not only do they provide us with oxygen to breathe, they also generate the starting materials for everything we eat. Rather than focusing on names and trivial details, this book shows how plants harvest energy in a way that self-regulates. Plants shift how they process light energy to maximize their productivity and minimize their exposure to dehydration. All of this regulation is carried out inside every plant on earth. In addition to plants, there are microbial primary producers that can harvest energy from a range of environmental sources so that no place on earth is devoid of life.