Concept:An ecosystem is a self-sustaining unit where biotic and abiotic components interact through key processes that maintain balance and function.
Explanation:The four processes—productivity, decomposition, nutrient cycling, and energy flow—are all essential for an ecosystem to be self-regulatory and self-sustained.
Productivity refers to the rate at which solar energy is converted into biomass by plants. It is measured as weight or energy per unit area.
Decomposition breaks down complex organic matter into simple inorganic forms by decomposers like earthworms. Steps include fragmentation, leaching, catabolism, humification, and mineralization.
Nutrient cycling, or biogeochemical cycles, ensures the cyclic flow of nutrients between biotic and abiotic components. Plants absorb nutrients, animals consume them, and decomposers return them to the soil.
Energy flow is the unidirectional transfer of energy from the sun through producers to consumers via food chains (grazing and detritus).
All four processes are interdependent and necessary for ecosystem functioning. Therefore, statements (a), (b), (c), and (d) are correct.
Answer:C. (a), (b), (c) and (d)