Final answer:
A food chain is a sequence showing how energy flows in an ecosystem, beginning with producers and moving up to primary, secondary, and tertiary consumers, ending with apex predators.
Step-by-step explanation:
A food chain is an ecological concept used to describe the passage of energy and nutrients through an ecosystem. It begins with producers, usually photosynthetic organisms like plants or phytoplankton, which harness energy from the sun. This energy is then transferred to primary consumers, typically herbivores, which feed on the producers. Secondary consumers, mainly carnivores, eat the primary consumers, and the sequence continues with tertiary consumers, carnivores who feed on secondary consumers. The apex predators sit at the top of the food chain, consuming tertiary consumers.
An example of a food chain could start with grass as the producer, which is eaten by a grasshopper (primary consumer). The grasshopper, in turn, is consumed by a frog (secondary consumer), which is then preyed upon by a snake (tertiary consumer), and finally, the snake could be eaten by an eagle (apex predator).
Ultimately, the energy that enters the ecosystem from sunlight is transformed into chemical energy through photosynthesis, moves up the food chain as organisms consume each other, and finally disperses as metabolic heat and substances that decomposers break down.