Solar Energy Flow in Ecosystems — NEET Biology
✅ Asked in NEET 2025Except for the deep sea hydro-thermal ecosystem, sun is the only source of energy for all ecosystems on Earth. Of the incident solar radiation less than 50 per cent of it is photosynthetically active radiation (PAR). We know that plants and photosynthetic bacteria (autotrophs), fix Sun's radiant energy to make food from simple inorganic materials. Plants capture only 2-10 per cent of the PAR and this small amount of energy sustains the entire living world. So, it is very important to know how the solar energy captured by plants flows through different organisms of an ecosystem. All organisms are dependent for their food on producers, either directly or indirectly. So you find unidirectional flow of energy from the sun to producers and then to consumers. Is this in keeping with the first law of thermodynamics?
NTA tests whether students understand that the sun is the primary energy source for all Earth ecosystems (except deep-sea hydrothermal vents), and only 2-10% of photosynthetically active radiation is captured by plants. Many students mistakenly think energy is recycled or multiplied through trophic levels, forgetting that energy FLOWS unidirectionally (sun → producers → consumers) and is lost at each step as heat. The key trap: confusing energy flow with nutrient cycling—nutrients cycle, but energy flows one way and depletes. Remember: plants capture a tiny fraction of solar energy, this energy sustains all life, and energy transfer follows the first law of thermodynamics (energy is conserved but transforms). This concept is fundamental for understanding ecosystem efficiency and food chains.
(NEET 2025) Given below are two statements: Statement I: The primary source of energy in an ecosystem is solar energy. Statement II: The rate of production of organic matter by photosynthesis in an ecosystem is called net primary productivity (NPP). In the light of the above statements, choose the most appropriate answer from the options given below:
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