Ecology is the scientific study of interactions between organisms and their environments, focusing on energy transfer. The environment includes biotic factors like living organisms and abiotic non-living factors like temperature and soil. Organisms exist at different levels of organization from individual to population to community to ecosystem to biosphere. Feeding relationships include producers, consumers at different trophic levels, and decomposers. Relationships can be symbiotic like mutualism, commensalism, or parasitism. Nutrients cycle through ecosystems like water, carbon, and nitrogen to maintain homeostasis. Toxins can biomagnify and increase in concentration up food chains.