Biology · Ecosystems · NEET
Yes. GPP is always greater than NPP. This is because plants always burn some of the food they make in respiration (R). Since R is always a positive amount, NPP = GPP - R must be smaller than GPP. GPP and NPP can never be equal. NEET 2020 tested exactly this: the correct answer is 'GPP is always more than NPP'.
GPP is the TOTAL organic matter (food) made by plants in photosynthesis. NPP is the food LEFT OVER after plants use part of it for their own respiration. Formula: GPP - R = NPP. GPP is the gross (full) amount; NPP is the net (remaining) amount that heterotrophs can eat.
NPP is the biomass available for consumption by heterotrophs, that is herbivores and decomposers. Only the NPP (not the GPP) can pass to the next trophic level, because plants have already spent part of the GPP on their own respiration. This is why NPP matters for energy flow in NEET questions.
GPP. Gross Primary Productivity is defined as the rate of production of organic matter DURING photosynthesis. NEET 2025 gave a trap statement calling this 'net primary productivity' - that statement was marked INCORRECT because photosynthesis defines GPP, not NPP.
No, never. They are different because of respiration losses (R). If someone says GPP and NPP are 'one and the same', that is wrong (a NEET 2020 trap option). They are only linked by the equation GPP - R = NPP.
Both are rates, so their unit carries time. Productivity is expressed in g m-2 yr-1 or (kcal m-2) yr-1. NEET 2025 asked this: the correct unit is (kcal m-2) yr-1. A unit without 'per year' (like kcal m-2) measures production or biomass, not productivity.
In relation to gross primary productivity and Net primary productivity of an ecosystem, which one of the following statements is correct?
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). Choose the most appropriate answer.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
GPP - R = NPP, where R is respiration losses (the part of GPP that plants use up in their own respiration). This is the exact NCERT equation for the Ecosystem chapter.
NPP is the biomass actually available for consumption by heterotrophs (herbivores and decomposers). Plants have already used part of GPP for respiration, so only NPP can move up the food chain.
GPP is always higher. Because respiration (R) is always subtracted, NPP is always smaller than GPP. They are never equal.
Yes. NCERT says primary productivity depends on the plant species in an area, plus environmental factors, nutrient availability, and photosynthetic capacity of plants. So it varies between ecosystem types.
About 170 billion tons (dry weight) of organic matter per year. Of this, oceans contribute only about 55 billion tons even though they cover about 70 percent of Earth's surface.
