An ecosystem includes all living organisms (biotic) and non-living factors (abiotic) in an area.
Food chains show energy transfer: producer → primary consumer → secondary consumer → tertiary consumer. Only ~10% of energy is transferred between trophic levels. Energy is lost through respiration, excretion, and not all parts being eaten.
Decomposers (bacteria, fungi) break down dead matter, recycling nutrients back to the soil.
Biomass pyramids show the mass of living material at each trophic level. They get smaller higher up because energy is lost.