A protected area that conserves a large ecosystem with core-buffer-transition zones is a

(a) national park

(b) biosphere reserve

(c) wildlife sanctuary

(d) reserve forest

Correct answer: (b) Biosphere reserve

Biosphere reserves are large, landscape-scale protected areas designed to conserve entire ecosystems using a three-zone model:

• Core zone: Strictly protected natural area for conserving biodiversity and ecological processes; no human interference except monitoring/research.
• Buffer zone: Surrounds the core; limited activities like research, education, eco-tourism, and habitat management that do not harm the core.
• Transition zone: Outermost area where local communities live and practice sustainable agriculture, forestry, and livelihoods, demonstrating people–nature harmony.

This core–buffer–transition design lets biosphere reserves conserve biodiversity and support sustainable development. Examples in India include the Nilgiri, Nanda Devi, and Sunderban Biosphere Reserves.

Why the other options are not correct

• (a) National park: A strictly protected area for ecosystem and wildlife conservation; human activities are highly restricted. While some parks have surrounding buffers, the formal three-zone biosphere model is not their defining feature.
• (c) Wildlife sanctuary: Protects particular species/habitats with relatively more permitted human activity than national parks; does not require core–buffer–transition zoning.
• (d) Reserve forest: A legal category of forest with restricted use under forest laws; it is not a designated ecosystem-scale conservation area with the tri-zonal scheme.

Final answer: (b) Biosphere reserve.