Answer: The correct answer for the fill in the blank is - Flow of energy in an ecosystem.
A food chain is a series of different trophic levels ( like producers, primary consumers, secondary consumers) in an ecosystem, which depicts how organisms obtain energy by consuming other organisms.
A food web is an interconnected network of different food chains representing flow of energy and matter within an ecosystem.
The different arrows in a food chain and food web represent organisms being eaten by other organisms, thereby representing flow of energy within an ecosystem.
