Which is correct about amensalism?

The correct answer is Option (1) → One species is harmed and other is unaffected.

Option (1) One species is harmed and other is unaffected. — Correct. In amensalism, one species is harmed while the other is unaffected (−/0). Among the population interactions, mutualism is +/+, competition −/−, predation and parasitism +/−, and commensalism +/0.

Option (2) One species is benefitted and other is unaffected. — Incorrect. One species benefiting while the other is unaffected (+/0) is commensalism, as with an orchid on a mango branch.

Option (3) One species is harmed and other is benefitted. — Incorrect. One species benefiting at the cost of the other (+/−) is predation or parasitism.

Option (4) Both the species are benefitted. — Incorrect. Both species benefiting (+/+) is mutualism, as in lichens or mycorrhizae.

Note: A similar question was also asked in CUET (UG) 2025 on 20-05-2025 (Slot 1).

NCERT Extract:
Population Interactions – “… Both the species benefit in mutualism and both lose in competition in their interactions with each other. In both parasitism and predation only one species benefits (parasite and predator, respectively) and the interaction is detrimental to the other species (host and prey, respectively). The interaction where one species is benefitted and the other is neither benefitted nor harmed is called commensalism. In amensalism on the other hand one species is harmed whereas the other is unaffected.”