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Biology · 2026 · 2 marks
CBSE 2026 · Region 2 · Set 3 · Q20
(a) Explain the type of interaction between: (i) Egret and Cattle (ii) Cuckoo and Crow
(a)
Explain the type of interaction between :
(i)
Egret and Cattle
(ii)
Cuckoo and Crow
OR
(b)
Biodiversity exists at various levels within an ecosystem. Explain biodiversity at genetic and ecological level.
Marking-scheme solution
(i)
Commensalism , Egret is benefitted and cattle neither benefitted nor harmed
/ as the cattle move they stir up and flush out insects from vegetation which might be difficult for egrets to find and catch.
(ii)
Brood Parasitism, The Cuckoo lays its eggs in the nest of the crow as the
eggs resemble the eggs of crow the crow (host) incubates the eggs.
Genetic level: A single species might show high diversity at the genetic level over its distributional range like Medicinal plant Rauwolfia vomitoria shows genetic diversity in terms of potency of concentration of active chemical reserpine / India has more than $\displaystyle 50,000$ genetically different strains of rice / India has more than $\displaystyle 1000$ varieties of mango.
Ecological level: At ecosystem level India has deserts /rain forests / mangroves / coral reefs / wetlands /estuaries / Alpine meadows that shows a greater ecosystem diversity than Scandinavian countries like
Norway
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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.