NCERT · Class 10 · Science · Our EnvironmentWhat is an ecosystem? Explain its various components with examples. Also, describe the flow of energy through different trophic levels in an ecosystem with the help of a neat diagrammatic description and the 10% law.

Definition of Ecosystem\nAn ecosystem is a self-sustaining structural and functional unit of the biosphere, consisting of a community of living organisms (biotic component) interacting with each other and with their non-living physical environment (abiotic component).

Components of an Ecosystem

1. Biotic Components: These include all the living organisms present in an ecosystem. They are broadly classified into three categories based on how they obtain their food:

   • Producers (Autotrophs): Green plants and blue-green algae that can manufacture their own food through photosynthesis using solar energy.
   • Consumers (Heterotrophs): Organisms that depend directly or indirectly on producers for food. They are further divided into herbivores (plant-eaters like deer, cows), carnivores (meat-eaters like lions, tigers), omnivores (plant and meat eaters like humans, bears), and parasites.
   • Decomposers (Saprotrophs): Microorganisms like fungi and bacteria that break down complex organic substances from dead remains and waste products into simple inorganic substances, returning nutrients to the soil.

2. Abiotic Components: These are the non-living physical and chemical factors of the environment that affect the survival, growth, and reproduction of living organisms. Examples include temperature, light, rainfall, soil, minerals, wind, water, and humidity.

Flow of Energy and the 10% Law

• The flow of energy in an ecosystem is always unidirectional. Energy flows from the sun to producers, then to herbivores, then to carnivores, and finally to decomposers. Energy captured by autotrophs does not revert back to the solar input; it passes progressively through the food chain.
• Lindeman's 10% Law: According to this law, only 10% of the energy entering a particular trophic level is available for transfer to the next trophic level. The remaining 90% is lost to the environment as heat during metabolic activities like respiration, digestion, and movement.
• For example, if green plants (producers) absorb 10,000 J of solar energy, only 1,000 J of energy is stored as food. When herbivores eat these plants, they receive only 100 J. Subsequent carnivores at the next level receive only 10 J, and tertiary carnivores get just 1 J. This rapid decrease in available energy limits the number of trophic levels in a food chain to usually four or five.