A – AbioticB – BiodiversityC – Carbon cycleD – DecomposerE – Energy flowF – Food chainG – Greenhouse gasesH – HabitatI – Invasive speciesJ – JungleK – Keystone speciesL – Litter (organic)M – MicroorganismN – Nutrient cycleO – OrganismP – PhotosynthesisQ – Quaternary consumerR – RespirationS – SymbiosisT – Trophic levelU – Understory (forest layer)V – VegetationW – Water cycleX – Xerophyte (plants in dry regions)Y – Yield (of crops in ecosystems)Z – Zooplankton