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Biology Question 100 – NEET-UG 2025

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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 during 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 :

Recall the fundamental source of energy for most ecosystems on Earth.

Step 1: Evaluate Statement I✦ Active

Statement I states that the primary source of energy in an ecosystem is solar energy. This is generally true for most ecosystems on Earth, where producers (like plants and algae) capture solar energy through photosynthesis, forming the base of the food web. While some exceptions exist (e.g., chemosynthetic ecosystems), solar energy is overwhelmingly the primary source for the vast majority of ecosystems.

Step 2: Evaluate Statement II○ Expand

Statement II defines net primary productivity (NPP) as the rate of production of organic matter during photosynthesis in an ecosystem. This definition is incorrect. The total rate of production of organic matter during photosynthesis is called Gross Primary Productivity (GPP). Net Primary Productivity (NPP) is the GPP minus the energy lost by producers during respiration (R), i.e., NPP=GPP−R. NPP represents the biomass available for consumption by heterotrophs.

💡 Teacher's Secret Hint

Remember the difference between GPP (total production) and NPP (production remaining after respiration).

Step 3: Conclude based on evaluation○ Expand

Based on the evaluation, Statement I is correct, and Statement II is incorrect. Therefore, the most appropriate option is (3).

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