NEET 2025 Zoology Question 170 Solution

Principles of ecosystem energetics:

• • Solar radiation is the primary driving energy source for nearly all terrestrial and aquatic ecosystems on Earth (except deep-sea hydrothermal vents).
• • Autotrophic producers (plants, phytoplankton) capture 2–10% of Photosynthetically Active Radiation (PAR) through photosynthesis, converting radiant energy into chemical bond energy.
• • This energy flows progressively from producers to primary consumers (herbivores), then to secondary and tertiary consumers (carnivores).
• • At each trophic transfer, approximately 90% of energy is dissipated as metabolic heat ($10\%$ law of Lindeman), meaning energy cannot be recycled or flow in reverse back to the sun.
• • Thus, energy flow is strictly unidirectional. Statement I is completely CORRECT.

Physical laws governing biological systems:

• • The Second Law of Thermodynamics states that any spontaneous physical or chemical process results in an increase in the entropy (disorderliness) of the universe.
• • Living organisms and ecosystems maintain highly organized, low-entropy states.
• • To prevent entropic decay into disorder and death, ecosystems require a continuous, uninterrupted influx of energy from the sun to synthesize complex biomolecules and pump ions against gradients.
• • NCERT explicitly emphasizes: "Ecosystems are not exempt from the Second Law of thermodynamics."
• • Therefore, claiming ecosystems are exempted is completely INCORRECT. Statement II is FALSE.

Statement I is correct, but Statement II is incorrect. This corresponds to Option (3).