Population Interactions NEET 2026: Answer and Sign Table

What is the answer to the Population Interactions NEET 2026 question?

Option D is correct: A-III, B-I, C-II, D-IV. The Population Interactions NEET 2026 question comes from NEET UG 2026, held on 21 June 2026, Code-50, Biology. Its medium difficulty label belongs to the supplied question bank, not an official NTA rating.

Match each outcome in List-I with an interaction in List-II. Keep statement letters separate from answer-option letters.

List-I, statement letters:

• Statement A: Each species experiences a disadvantage.
• Statement B: One gains at the other’s expense.
• Statement C: Each species gains.
• Statement D: One gains without changing the other’s outcome.

List-II, interaction numerals:

• I: Predation.
• II: Mutualism.
• III: Competition.
• IV: Commensalism.

Answer options:

How do NCERT interaction signs give every match?

Write two signs for each statement, identify the interaction, then assign its Roman numeral. The supplied official solution uses the interaction-sign table in NCERT Class 12 Biology, Organisms and Populations, identified there as Table 13.1. Each sign records the effect on one species, not whether the relationship sounds helpful overall.

Every relationship needs two signs. A benefit to one species alone cannot settle the classification.

Statement A: both experience a disadvantage. Limited shared resources impose costs on both competing populations. Each has reduced access to resources because the other population also uses them.

Statement B: one gains while the other is harmed. The predator obtains nutrition, while the prey is harmed or killed. That matches predation among the supplied choices.

If the harmed species is listed first, the signs reverse order. The interaction remains the same: $(-,+)$

Parasitism also has benefit-and-harm signs. Predation is the matching choice here because parasitism is absent from List-II. These signs are not exclusive to predation.

Statement C: both gain. In mycorrhiza, fungal partners help plant roots obtain minerals, while the plant supplies organic nutrients to the fungi. This exchange benefits both partners.

Statement D: one gains and the other is unaffected. An epiphyte gains support from its host tree; the tree is unaffected in this NCERT example. Gaining support does not mean the epiphyte extracts nutrients from the tree.

The complete sequence is A-III, B-I, C-II, D-IV. Only option D matches all four entries, not just the first pair.

Why does checking only one species produce wrong option A?

Option A correctly assigns A-III and C-II, but incorrectly assigns B-IV and D-I. It swaps predation and commensalism. This error follows from noticing that one species benefits in both B and D, then assigning names without checking the second species.

The decisive difference is the second sign. Predation requires harm to the other species; commensalism requires no effect on it.

Write both signs beside every statement before looking for its Roman numeral. Record this mistake as “omitted second-species check”, not “carelessness”: Fix errors before your next mock.

Under the NEET marking scheme, a correct response earns four marks; a wrong response earns minus one. That creates a five-mark difference between the outcomes, not a five-mark wrong-answer penalty:

Can competition cause unequal losses?

Yes. Competition requires harm to both populations, not equal losses. The following set contains three original same-chapter practice questions, not additional verified PYQs.

Question 1: Two herbivore species use the same limited grass supply. Each obtains less food in the other’s presence than it would alone, although one loses more. Which interaction applies?

Answer: B, competition. Species 1 has reduced food access, and species 2 also has reduced access. The signs record the direction of each effect, not equal numerical magnitudes:

Can benefit-and-harm signs alone distinguish predation from parasitism?

No. Both interactions share these signs; biological details distinguish them. The sign table records benefit and harm, not a unique name for every relationship.

Question 2: An organism gains nutrients from a living host and harms it. If only the following signs are provided, can predation and parasitism be distinguished? $(+,-)$

Answer: C. The host description adds biological detail, but signs alone cannot distinguish them. In the PYQ, B-I follows because predation is the relevant available List-II entry, not because these signs are exclusive to predation.

How do mycorrhiza and an epiphyte differ?

Mycorrhiza is mutualism; the stated epiphyte–tree association is commensalism. The difference is whether both partners benefit or only one does.

Question 3: Classify a plant–mycorrhizal fungus association where both exchange useful resources, and an epiphyte–tree association where the epiphyte gains support while the tree is unaffected, respectively.

Answer: A. The plant benefits from fungal assistance with mineral uptake; the fungus receives organic nutrients from the plant. $(+,+)\to \text{Mutualism}$

The epiphyte gains support; the stipulated effect on the tree is zero. Only the epiphyte benefits: $(+,0)\to \text{Commensalism}$

Cover the solutions and retrieve these pairs before checking:

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