The correct answer is option 3: one organism to another. The food chain is a process that illustrates the transfer of energy from one organism to another in an ecosystem. It represents the flow of energy through different trophic levels, starting from producers (plants or algae) who generate food through photosynthesis, and then transferred to primary consumers (herbivores), secondary consumers (carnivores), and so on. This transfer of energy occurs as organisms eat and are eaten by other organisms. Each step in the food chain represents a feeding relationship and energy transfer between organisms. Therefore, the food chain is a crucial component of ecological systems as it demonstrates how energy circulates and is passed along within an ecosystem.