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Biology · 2025 · 2 marks
CBSE 2025 · Region 1 · Set 1 · Q18
Student to attempt either option-(A) or (B): (A) Analyse the following ecosystems and discuss, which will be more productive in terms of primary…
Student to attempt either option-(A) or (B) :
(A)
Analyse the following ecosystems and discuss, which will be more productive in terms of primary productivity : A young forest, a natural old forest, a shallow polluted lake.
OR
(B)
Differentiate between Net primary productivity and Gross primary productivity in an ecosystem.
Marking-scheme solution
Natural old forest will be more productive ,
As it contains more biomass or high biodiversity which will trap and store solar radiation in form of biomass , Young forest is still developing and contain fewer trees will not capture solar radiations as much as old forest so productivity is low , Shallow polluted lake contains less number of producers and high amount of dead organic matter so productivity is less in comparison to natural old forest.
| Net Primary Productivity | Gross Primary Productivity |
| i) Gross primary productivity minus respiration losses (R) is the net primary productivity. | i) Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. |
| ii) It is the available biomass for the consumption to heterotrophs. | ii) A considerable amount of gross primary utilised by plants respiration. |
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CBSE Class 12 Biology past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.