In a food chain, the sun is often referred to as the ‘primary energy source.’ It plays a crucial role in the ecosystem as it provides the energy required for photosynthesis, which is the process that allows plants to convert sunlight into chemical energy in the form of glucose.
Without the sun, there would be no plants, and without plants, the entire food chain would collapse. Herbivores eat the plants, and then carnivores eat the herbivores, creating a complex web of life dependent on that initial energy provided by the sun.