Sunlight is energy, and plants use this energy to turn water and carbon dioxide into plant food. This process is called “photosynthesis”. Energy passes from one animal to another as they eat plants or one another. This flow of energy from one living thing to another is called a “food chain energy begins with Sunlight Because plants make so much energy, they are called “producers”. Their ability to use sunlight to make food makes them a very important source of energy for other living things.