Photosynthetic refers to a process by which green plants and some other organisms convert light energy into chemical energy, using sunlight as an energy source. During photosynthesis, these organisms use carbon dioxide from the atmosphere and water from their roots to produce glucose (a sugar) that serves as food for the plant or other organism. Oxygen is released as a byproduct of this process. Photosynthetic organisms are essential for life on Earth because they provide oxygen, which is necessary for most living creatures to survive, and they form the base of the food chain in many ecosystems.