Ecological Pyramids: Numbers & Biomass — NEET Biology

Correct answer: C — S1, S2, S3, S4 and S5

Let's evaluate each statement to identify those that are NOT correct: S1: Energy flow in an ecosystem is typically bidirectional, allowing for recycling of energy between different trophic levels. This statement is NOT correct. NCERT clearly states, 'There is unidirectional movement of energy towards the higher trophic levels and its dissipation and loss as heat to the environment.' Energy cannot be recycled back to lower trophic levels. S2: In a forest ecosystem, the pyramid of number is always upright, similar to a grassland ecosystem, maintaining a broad base of producers. This statement is NOT correct. A tree-based ecosystem, which is a type of forest, has an inverted pyramid of number ('If you were to count the number of insects feeding on a big tree what kind of pyramid would you get?'). Therefore, it is not always upright. S3: The inverted pyramid of biomass observed in oceanic ecosystems is primarily due to the very large standing crop and slow turnover rate of phytoplankton. This statement is NOT correct. The inverted biomass pyramid in the sea is due to the *low* standing crop and *high* turnover rate of phytoplankton, with the biomass of larger consumers (fishes) far exceeding that of producers. NCERT states, 'The pyramid of biomass in sea is generally inverted because the biomass of fishes far exceeds that of phytoplankton.' S4: Ecological pyramids are universally ideal representations, as they flawlessly account for complex food webs and organisms operating at multiple trophic levels. This statement is NOT correct. NCERT lists these as limitations: 'it does not take into account the same species belonging to two or more trophic levels. It assumes a simple food chain...it does not accommodate a food web.' S5: Primary productivity in the oceans accounts for a larger fraction of the total biosphere's net primary productivity compared to land, owing to their vast area. This statement is NOT correct. NCERT states, 'The annual net primary productivity of the whole biosphere is approximately 170 billion tons (dry weight) of organic matter. Of this, despite occupying about 70 per cent of the surface, the productivity of the oceans are only 55 billion tons. Rest of course, is on land.' This means land productivity is much higher (115 billion tons) than ocean productivity (55 billion tons). Therefore, all statements S1, S2, S3, S4, and S5 are NOT correct. This question tests a broad understanding of energy flow principles, pyramid shapes in different ecosystems, and the known limitations of ecological pyramids.