An ecosystem is a community of living organisms interacting with their physical environment as a functional unit. The living components, called biotic factors, include producers, consumers, and decomposers along with all of their interactions. The nonliving components, called abiotic factors, include temperature, sunlight, water, soil, wind, and minerals. Together, these elements create the conditions that determine which organisms can thrive in a given place, whether on land, in fresh water, or in the ocean.
Net primary productivity, or NPP, measures the rate at which producers in an ecosystem store energy as biomass after accounting for their own cellular respiration. The relationship is expressed as \( NPP = GPP - R \), where GPP represents gross primary productivity and R represents respiration. Ecosystems with high NPP, such as tropical rainforests and estuaries, capture and store far more energy than ecosystems with low NPP, such as deserts or the open ocean.
Ecosystems depend on the continuous movement of essential elements through biogeochemical cycles. The carbon cycle exchanges carbon among the biosphere, atmosphere, oceans, and geosphere through processes like photosynthesis, respiration, and combustion. Photosynthesis converts carbon dioxide and water into glucose and oxygen using light energy, while cellular respiration breaks down glucose with oxygen to release energy, carbon dioxide, and water; these two processes are complementary, with the products of one serving as the reactants of the other. The nitrogen cycle converts nitrogen between its various chemical forms as it circulates through the atmosphere, soil, and organisms. The water cycle, also called the hydrological cycle, describes the continuous movement of water through evaporation, condensation, precipitation, runoff, and infiltration between Earth's surface and its atmosphere.