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Biology · 2026 · 2 marks
CBSE 2026 · Region 1 · Set 3 · Q21
(a) (i) What is primary productivity of an ecosystem and how is it expressed? (ii) Explain the equation given below: NPP = GPP - R 1 (b) Biodiversity…
(a)(i)
What is primary productivity of an ecosystem and how is it expressed ?
(ii)
Explain the equation given below : NPP = GPP - R $\displaystyle 1$
(b)
Biodiversity conservation is crucial for maintaining ecological balance and ensuring the survival of future generations. Describe four advanced ex-situ methods used for conservation of biodiversity.
Marking-scheme solution
(i)
• Primary Productivity -It is the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis.
• It is measured in terms of- energy / Kcal per m$\displaystyle ^2$ per year / weight / g per m$\displaystyle ^2$ per year.
(ii)
Gross primary productivity minus respiratory losses is the net primary productivity /
NPP - Net Primary Productivity
GPP -Gross Primary Productivity
R-Respiratory losses.
Four types of advanced techniques of ex – situ conservation of biodiversity are-
-Gametes or pollens of threatened species can be preserved in viable and fertile conditions for long periods using cryopreservation techniques or at $\displaystyle -196^{\circ}$C
-Eggs can be fertilized in vitro.
-Plants can be propagated by tissue culture method
-Seeds of different genetic strains of commercial importance can be stored in seed banks.
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CBSE Class 12 Biology past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.