The primary source of energy for all living organisms is the sun. Solar energy is the driving force behind photosynthesis, the process by which plants, algae, and some bacteria convert sunlight into chemical energy stored in glucose. This energy then flows through the food chain, supporting herbivores, which in turn sustain carnivores. Additionally, many ecosystems rely directly on solar power for growth and survival. While other sources of energy, like geothermal and chemical, exist, the sun remains fundamental for life on Earth, sustaining both plant and animal life.