The universal source of energy in living organisms is sunlight, which is harnessed through the process of photosynthesis. This was primarily demonstrated by plants, algae, and some bacteria that convert solar energy into chemical energy in the form of glucose.
Through photosynthesis, these organisms take in carbon dioxide from the atmosphere and water from the soil. Using sunlight, they transform these ingredients into glucose, a simple sugar, and oxygen is released as a byproduct. This process is crucial not only for the plants themselves but for all living organisms on Earth, as it forms the base of the food chain.
Once glucose is produced, it can be utilized by plants for energy or stored for later use. When animals eat these plants, they convert the stored chemical energy from glucose into ATP (adenosine triphosphate) through cellular respiration, which is then used for various cellular processes requiring energy. Thus, sunlight is fundamentally important as it initiates a series of energy transformations that support all life on Earth.