A food chain is a succession of organisms that eat other organisms and are being eaten by other organisms occupying different levels called the trophic levels. The first trophic level is occupied by the producers which include the plants, the second level includes the herbivores, the third level and subsequent levels represent the carnivores. The plants are called the producers since they can prepare their own food and the other organisms dependening on them are called the consumers.
According to the Ten percent law of energy transfer, only ten percent of the energy is transferred to each trophic level and the remaining is lost during the transfer. If the producers have 3000 calories of energy, the primary consumers obtain 300 calories from them. The secondary producers and tertiary consumers obtain 30 calories and 3 calories only.