Energy flows through an ecosystem in a one-way, unidirectional stream, starting from the primary producers and moving through various consumers at different trophic levels. The process begins with the Sun, which provides solar energy that is captured by primary producers—mainly green plants and algae—through photosynthesis. These producers convert solar energy into chemical energy stored in organic molecules like glucose
. From there, energy transfers to primary consumers (herbivores) when they eat the producers. Secondary consumers (carnivores that eat herbivores) and tertiary consumers (higher-level carnivores) then obtain energy by consuming organisms from the level below. This sequence of energy transfer is called a food chain, and the interconnected feeding relationships form a food web
. At each step in the food chain, energy is lost primarily as heat due to metabolic processes such as cellular respiration. Typically, only about 10% of the energy at one trophic level is passed on to the next level, which limits the number of trophic levels in most ecosystems to around five or fewer
. This loss of energy explains why there are usually fewer top predators than producers in an ecosystem. Energy flow is governed by the laws of thermodynamics and is always unidirectional—from the Sun to producers and then through consumers—without recycling back to the Sun. This flow supports ecosystem structure and function, maintaining ecological balance
. In summary, energy flows through an ecosystem as follows:
- Solar energy is captured by primary producers via photosynthesis.
- Energy moves to primary consumers when they eat producers.
- Energy continues to secondary and tertiary consumers through predation.
- At each trophic level, energy is lost as heat, reducing the amount passed on.
- The flow is unidirectional and forms the basis of food chains and food webs.
This process sustains life and drives ecosystem productivity and dynamics
