Energy flow in an ecosystem refers to the one-way movement of energy through the living organisms — from the sun to producers and then to various consumers.

Step-by-step flow:

1. Sunlight is the main source of energy for all ecosystems.
2. Producers (plants, algae) capture solar energy by photosynthesis and convert it into chemical energy (food).
3. Primary consumers (herbivores) eat the producers and get the stored energy.
4. Secondary consumers (carnivores) eat the herbivores.
5. Tertiary consumers (top carnivores) eat other carnivores.
6. Decomposers (bacteria, fungi) break down dead organisms and release nutrients back into the soil — but do not recycle energy.

Important points:

• Energy flows in a single direction — it is not recycled.
• At each step (called a trophic level), a lot of energy (about 90%) is lost as heat (due to life processes like respiration).
• Only about 10% of the energy is passed on to the next trophic level — this is called the 10% Law.

In short:

Sun → Producers → Herbivores → Carnivores → Decomposers