Ecology is the study of interactions between organisms and their environment. Ecologists study both abiotic (non-living) and biotic (living) environmental factors that influence organisms. Key abiotic factors include light, water, temperature, and soil properties. Biotic factors include habitats, ecological niches, populations, communities, food webs, and ecosystems. Energy flows through ecosystems in food chains and is lost at each trophic level, forming pyramids of numbers, biomass, and energy. Carbon and nitrogen cycles are essential for providing these elements to living things. Parasitism, like malaria, harms hosts to benefit parasites. Malaria is transmitted between humans and Anopheles mosquitoes.