Explained answer:
A food chain describes the flow of energy from one organism to another in an ecosystem. For example, in a grassland ecosystem, a food chain could be as follows: grass is eaten by a rabbit, which is eaten by a fox. In this food chain, the grass is the producer, the rabbit is the primary consumer, and the fox is the secondary consumer. As the fox eats the rabbit, it obtains the energy that the rabbit got from the grass. This energy flow is what sustains the ecosystem.