The sun--solar energy--is at the heart of the cycle of life, with all the sustenance relationships referred to as the food web. The sun is the ultimate source of energy for animals, but its energy must be harnessed by plants before it can be used by animals. Animals get energy by processing complex foods.
For all organisms, the sun, or solar radiation, is the ultimate source of energy. Plants are primary producers of energy from the sun. Plants use sun, chlorophyll, water, carbon dioxide and nutrients to manufacture glucose, an alternate form of energy. Glucose stores heat and energy. Because animals cannot produce energy directly from the sun, they must eat plants or other animals that eat plants, and acquire energy, either directly or indirectly, from glucose. Animals that eat plants exclusively are called herbivores. Animals that only eat meat are called carnivores. Omnivores are animals that eat both plants and meat. The most efficient and most concentrated energy is consumed at the lowest part of the food chain: directly from plants.
Energy and Herbivores
Herbivores are the animals at the bottom of the animal food chain. These animals eat plants to survive. Herbivores are one step away from the ultimate source of energy, the sun. Herbivores have digestive systems that allow them to process all types of plants, including grasses. Cows, sheep, giraffes and elephants are herbivores. Herbivores require an abundant intake of energy to stay alive. Many herbivores eat, or graze, all day.
Energy and Omnivores
Omnivores are animals that eat plants and other animals. Omnivores generally eat only fruits and vegetables, and cannot digest grasses. Omnivores also eat animals that are herbivores. These omnivores kill and eat their own food. Others are scavengers, eating carrion or decomposing meat. Some omnivores are opportunists. They eat whatever they can find, including berries, roots, fruit, eggs and the young of other animals. In the food chain, omnivores are two steps away from the ultimate source of energy--the sun. Humans and bears are animals that are omnivores.
Energy and Carnivores
Carnivores, animals that eat other animals, are the last step in the food chain, and are the farthest away from the ultimate source of energy. Predators--like lions, wolves, hawks and other animals that kill prey and eat their meat--are carnivores. Carnivores eat herbivores, and sometimes eat omnivores and other carnivores. Although they are at the least efficient end of energy-use in the food chain, carnivores are essential in the ecosystem because they prevent overpopulation by other animals.
Energy from the sun is the primary source of energy for the earth's ecosystem. The sun's energy is collected and processed by plants through photosynthesis and converted into food for animals. Without the sun, animals would not exist. Food is stored energy and essential elements like carbon, nitrogen and hydrogen. Energy--food--is passed from producers, like plants, to consumers--animals. Through the process of decomposition, energy is dispersed to producers through the soil. Only about 10 percent of the energy in one level is transferred to the next level, however; for example, from plants to herbivores. Because such a small percentage of energy is transferred between levels, carnivores are the final step in the energy pyramid; there would not be enough energy available to support another level of consumers.