Energy Flow & Trophic Levels — NEET Biology

Correct answer: C — S1, S2, S4, and S5 only

Let's evaluate each statement: S1: The base of an energy pyramid represents the producers, and each bar indicates the amount of energy present at that trophic level annually per unit area. This statement is correct. NCERT states: 'The base of each pyramid represents the producers or the first trophic level... Each bar in the energy pyramid indicates the amount of energy present at each trophic level in a given time or annually per unit area.' S2: Energy pyramids can never be inverted because a significant amount of energy is lost as heat at each successive trophic level, adhering to the Second Law of Thermodynamics. This statement is correct. NCERT mentions: 'Pyramid of energy is always upright, can never be inverted, because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step.' It also states, 'Further, ecosystems are not exempt from the Second Law of thermodynamics.' S3: The transfer of energy from one trophic level to the next strictly follows the 10% law, typically allowing for up to six or seven trophic levels in a grazing food chain. This statement is incorrect. While the 10% law is followed, it *restricts* the number of trophic levels, rather than allowing for many. NCERT states: 'The number of trophic levels in the grazing food chain is restricted as the transfer of energy follows 10 per cent law'. More than 4-5 levels are very rare due to severe energy loss. S4: Similar to pyramids of number and biomass, the pyramid of energy does not account for decomposers or organisms occupying multiple trophic levels simultaneously. This statement is correct. NCERT lists limitations for 'ecological pyramids' generally: 'it does not take into account the same species belonging to two or more trophic levels...it does not accommodate a food web. Moreover, saprophytes are not given any place in ecological pyramids'. These apply to all types of ecological pyramids. S5: Photosynthetically Active Radiation (PAR) constitutes less than 50% of the incident solar radiation, of which plants typically capture 2-10%. This statement is correct. NCERT states: 'Of the incident solar radiation less than 50 per cent of it is photosynthetically active radiation (PAR). We know that plants... capture only 2-10 per cent of the PAR'. Therefore, statements S1, S2, S4, and S5 are correct. This question tests the understanding of the characteristics of energy pyramids, the 10% law, and the general limitations of ecological pyramids.