The ultimate source of energy for living things is the Sun. Plants and other photosynthetic organisms take the energy from sunlight to make glucose. This energy passes to other organisms through the food chain.
Food, which is the source of energy for all living things, originated in the transformation of carbon dioxide and water in the presence of sunlight. This process, called photosynthesis, changes light energy into fuel in the form of glucose for the plant. Most ecosystems have plants as their primary producers.
Consumers cannot make their own food from sunlight, so they must eat other organisms to obtain their energy. Primary consumers are generally the herbivores that feed on plants. Secondary consumers eat the primary consumers, and tertiary consumers ingest secondary consumers. When they die, organisms transfer their energy to the decomposers.