The correct answer is (a), (b), (c) and (d). Explanation & Key Takeaways: Ecosystem: • An ecosystem is the unit of ecology. • An ecosystem is a self-sustained unit. • It consists of biotic and abiotic components such as plants, animals, water, and sunlight. • Here, all these components interact and thus form a functionally stable unit. • The components of the ecosystem are seen to function as a unit when we consider it in terms of Productivity, Decomposition, Energy flow, and Nutrient cycling. (a)Productivity: • It is one of the essential requirements for ecosystem function. • It is defined as the amount of solar energy utilized for food production. • It is biomass or organic matter produced per unit area over some time. • It is measured in weight or energy, and units are weight (gm–2) or energy (kcal m–2). • It depends on the plant species and the environment. (b)Decomposition: • It is a process in which complex organic molecules break into simple inorganic forms. • It occurs by decomposers. • An earthworm is an example of a decomposer. • The steps of decomposition comprise fragmentation, leaching, catabolism, humification, and mineralization. • Its rate is affected by chemical components of matter and climatic factors. (c)Nutrient cycling: • It is also known as biogeochemical cycles. • The cyclic flow of nutrients takes place within the ecosystem components. • The reservoir of nutrients on the earth's surface. • Plants use them and thus transfer them to animals, animals then die and this organic matter is thus decomposed by decomposers and thus again nutrients are released back into the soil (reservoirs). • Thus, the flow of nutrients is maintained. (d)Energy flow: • It is essential for maintaining ecosystem functioning. • It is the unidirectional flow of energy. • Plants being the producers utilize sun energy and convert it to chemical energy. • Consumers feed on the producers to obtain energy and transfer it to another trophic level of consumers. • It is transferred in the form of a food chain. • It is who eats whom. • It is a detritus and grazing food chain. • The Detritus food chain begins from dead organic matter in the soil. • The grazing food chain begins with the plants. Related Concepts: • Productivity is Gross primary productivity and net primary productivity. • Gross primary productivity is the amount of production of matter by plants. • Some energy is lost via respiration. • Net primary productivity is the available biomass for consumption by consumers. • GPP – R = NPP. • Decomposition steps are;- • Fragmentation is the breakdown of complex particles into simpler forms. • Leaching is the movement of these molecules down deep into the soil. • Catabolism is the breakdown of these simple complex molecules into an inorganic form. • Humification is an accumulation of humus on the matter so that it can be degraded by microbes. • Mineralization is the release of simpler inorganic molecules so that they can be utilized by plants.