Energy within an ecosystem flows in a continuous, irreversible one-way stream, originating from the radiant core of the Sun and traveling sequentially through living organisms. Ecologists trace this linear trajectory through food chains, which delineate who eats whom across distinct trophic levels. Autotrophic green plants and algae serve as primary producers, capturing solar energy to manufacture organic biomass. Herbivores, acting as primary consumers, feed directly upon producers to extract vital nutrients. In turn, carnivores and omnivores occupy higher tiers as secondary and tertiary consumers, culminating in apex predators who face no natural predators. Finally, when organisms die, decomposers such as microscopic bacteria and fungi break down organic detritus, returning essential minerals and chemical elements to the soil to nourish future generations of plants.