- Photosynthetic organisms (like plants and algae) convert light energy from the sun into chemical energy (sugars) through photosynthesis. - This chemical energy forms the base of most food chains. Herbivores obtain energy by eating plants, carnivores by eating herbivores, and so on. - While carbohydrates and fats are forms of stored chemical energy within organisms, and ATP is the molecule used for energy transfer within cells, the original energy captured by the ecosystem (for most ecosystems) comes from the sun.