Amensalism
அமென்சலிசம் (ஒன்றுக்கு பாதிப்பு)
Do not confuse Amensalism with Competition. In competition, both suffer. In amensalism, one organism is indifferent while the other is destroyed.
The idea
Amensalism is a negative-neutral interaction denoted as (-, 0). One species is harmed through the secretion of chemicals or physical interference, while the second species remains unaffected. A classic NCERT example is Penicillium secreting penicillin, which kills bacteria without the fungus gaining any direct benefit.
Why it matters
Often a byproduct of one species' metabolic activities that create an environment toxic or inhibitory to another species.
NEET lens
NEET expects you to identify the (-, 0) notation instantly. Memorize the Penicillium-bacteria example as it is the only one explicitly mentioned in NCERT. Do not overthink; if the interaction is not mutual, it is not competition or mutualism.
Clinical significance
Antibiotic production is the biological application of amensalism. When this mechanism fails in nature, pathogenic bacteria proliferate unchecked. Understanding this interaction is the foundation of clinical pharmacology.
Introduction
Amensalism is an interaction in which one species is harmed while the other is unaffected (−, 0).
Core concept
Example: Penicillium (a mould) secretes penicillin, which kills or inhibits the growth of bacteria, while the mould itself is not affected. This interaction is widely used in medical science for the production of antibiotics. Some plants also release chemicals that inhibit the growth of nearby plants. In NCERT's table of population interactions: mutualism (+, +), competition (−, −), predation (+, −), parasitism (+, −), commensalism (+, 0), amensalism (−, 0).
Go deeper
Amensalism and commensalism are both 'one-sided' interactions — one partner is unaffected (0) in both.
From Class 10
When a mould makes a chemical that kills bacteria nearby but the mould isn't affected, that is amensalism.