Biology · Organisms and Populations · NEET
NCERT uses (+, -) meaning Species A (the predator) benefits and Species B (the prey) is harmed. The order only tells you which species gets which sign; the interaction itself is a benefit-harm pair. In a match-the-column NEET question, read the sign next to each species carefully instead of memorising a fixed left-right order.
In both, exactly one species gains and one loses. The predator or the parasite benefits (+), while the prey or the host is harmed (-). The difference is only in the biology, not the sign: a predator kills and eats prey quickly, while a parasite lives on or in the host and harms it slowly. NEET exploits this: if a (+/-) question lists both, use another clue in the options; if only one is listed, that is the answer.
Both have a 0, meaning one species is unaffected. In commensalism the other species BENEFITS (+/0), for example an orchid growing on a mango branch. In amensalism the other species is HARMED (-/0), for example Penicillium releasing penicillin that kills bacteria. Trap: students swap these because both contain 0. Remember: commensalism has a plus, amensalism has a minus.
The 0 means that species is neither helped nor harmed by the interaction; its survival, growth, or reproduction is unchanged. Only two interactions carry a 0 in NCERT: commensalism (+/0) and amensalism (-/0). If a question shows a 0 for one species, the answer must be one of these two.
Competition is (-/-): both species lose because they compete for the same limited resource, so each one's growth or survival is reduced. There is no (0/0) row in NCERT Table 11.1, because two species with zero effect on each other are not considered an interaction.
No. Population attributes (density, natality, mortality, sex ratio, age distribution) describe a SINGLE population. Population interactions happen BETWEEN two different species and are a community-level idea. NEET has directly tested this: species interaction is not a population attribute.
If '+' sign is assigned to beneficial interaction, '-' sign to detrimental and '0' sign to neutral interaction, then the population interaction represented by '+' '-' refers to
Which one of the following population interactions is widely used in medical science for the production of antibiotics?
Amensalism can be represented as :
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Six: Mutualism (+/+), Competition (-/-), Predation (+/-), Parasitism (+/-), Commensalism (+/0), and Amensalism (-/0). These are the exact six NEET tests from.
Only mutualism is (+/+), where both species benefit. Every other interaction harms or leaves neutral at least one species.
Only competition is (-/-). Both species lose because they fight over the same limited resource.
Only two: commensalism (+/0) and amensalism (-/0). Both contain a 0 for the unaffected species.
Yes. Directly asked almost every year, often as a match-the-column or a fill-the-sign question. Learning the six-row table guarantees these easy marks.
