Biology · Organisms and Populations · NEET
Amensalism is (-, 0). One species is HARMED (that is the minus), and the other species is UNAFFECTED (that is the zero). It is NOT (+, 0). The (+, 0) sign pair belongs to commensalism, where one species gains and the other feels nothing. Simple rule: in both interactions one partner scores 0 (no change), but in amensalism the other partner LOSES, while in commensalism the other partner WINS.
Both have one species with a 0 (no effect). The difference is only in the second species. In amensalism the second species is harmed (-), so the pair is (-, 0). In commensalism the second species benefits (+), so the pair is (+, 0). Example: an orchid growing on a mango branch is commensalism (orchid gains, tree unaffected). A large tree whose shade suppresses small herbs below it is amensalism (herb harmed, tree unaffected).
In NEET 2018 the answer to 'which population interaction is used to make antibiotics' was Amensalism. A fungus like Penicillium secretes a chemical (an antibiotic) that kills or slows nearby bacteria. The bacteria are harmed (-), but the fungus itself is not affected by killing them (0). That gives (-, 0) = amensalism. It is NOT parasitism because in parasitism the harming species actually BENEFITS by living on the host, giving (+, -). Here the fungus gains no direct benefit from the bacteria, so there is no plus sign.
No. This is the exact trap. In amensalism the second species gets a 0, meaning no gain and no loss. If it gained something, the interaction would become predation or parasitism (+, -), not amensalism. Keep amensalism strictly as 'one loses, one feels nothing'.
Yes. Amensalism appears in the NCERT table of population interactions (Chapter 'Organisms and Populations') as the (-, 0) interaction, described in the line 'In amensalism one species is harmed whereas the other is unaffected.' NEET has repeatedly tested it, including 2016, 2018, 2021 and 2026, so it is high-yield and safe to prepare.
Which one of the following population interactions is widely used in medical science for the production of antibiotics?
Amensalism can be represented as:
If '+' sign is assigned to beneficial interaction, '-' sign to detrimental and '0' sign to neutral interaction, then the population interaction represented by '+' '-' refers to
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Amensalism is an interaction between two species where one is harmed and the other is not affected in any way. Its sign notation is (-, 0).
Antibiotic action is the NCERT/NEET example: Penicillium (a fungus) secretes a chemical that kills bacteria, harming the bacteria while the fungus stays unaffected. A larger tree whose shade suppresses smaller plants beneath it is another common textbook example.
In predation one species (predator) gains and the other (prey) is harmed, giving (+, -). In amensalism the harming species gains nothing; it is (-, 0). The presence or absence of a benefit (+) is the key difference.
Amensalism has been tested in NEET 2016, 2018 (antibiotics), 2021 (its sign), 2023 (match the interaction) and 2026, making it a repeatedly examined, high-yield topic.
No. Competition is (-, -) where both species are harmed. Amensalism is (-, 0) where only one is harmed and the other is unaffected.
