In which part of the cinchona plant, quinine occurs naturally?

The correct answer is D) Bark. Quinine is a cinchona alkaloid, and it accumulates mainly in the bark (cortex) of Cinchona trees, a genus of the Rubiaceae family native to the Andean slopes of South America. Bark is also the commercial source, which is why cinchona bark was historically extracted for antimalarial drugs.

Why the others are wrong:

• Root: Roots contain some alkaloids, but they are not the principal natural site of quinine and are not the commercial source.
• Fruit: The fruit is not the site of quinine accumulation.
• Seed: Seeds are not a source of quinine.

Core concept: plant secondary metabolites (alkaloids) are stored in specific tissues, and the medicinal part can differ from plant to plant. This links to the Mains theme of colonial plantation economies, since British cinchona cultivation in the Nilgiris and Darjeeling hills was driven by demand for malaria treatment.

Trap: Aspirants often pick Root by analogy with medicinal plants like ashwagandha, where the root is used. For cinchona, remember the bark.