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The nematode Myrmeconem… (Class 12 Biology SQP 2026-27, Q28)

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BiologyCBSE Class 12 · Sample paper, session 2026-27 · 3 marks · Short answer

CBSE Class 12 Biology sample paper 2026-27: question 28

From the official CBSE sample question paper for 2026-27, section C, question 28, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q28 · 3 marks · Short answerCompetency-basedOrganisms and Populations

The nematode Myrmeconema neotropicum lives inside the abdomen of certain tropical ants (Cephalotes atratus). Inside the ant's body, the nematode develops slowly without killing it. Once mature, it changes the color of the ant's abdomen to bright red, making it resemble a berry. Birds, mistaking it for a fruit, eat the ant. The nematode's eggs survive in the bird's digestive system and pass out in droppings, which other ants contact while foraging, starting the cycle again.

A. Why would harming the ant too early be disadvantageous for the nematode? (1)
B. How is natural selection playing a vital role in maintaining this interaction? (1)
C. What kind of ecological interaction is seen between nematode and ant? Define it in one sentence. (1)

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2026-27.

Hints

Open one hint at a time and try again before the next.

Hint 1

The nematode needs time and a bird to finish its life cycle.

Hint 2

Which nematodes would leave more offspring: those that kill early or those that wait?

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. A. If the ant dies too early, the nematode cannot complete its development or reach maturity. The ant's abdomen will also not be eaten by a bird, so the nematode's eggs will not be dispersed to new hosts.

    1 mark

  2. B. Natural selection favours nematodes that keep the ant alive until it is eaten by a bird. This ensures complete maturation and wide dispersal through bird droppings, so such nematodes leave more offspring. Only the red-bellied infected ants are eaten, which also spares the uninfected ants.

    1 mark

  3. C. The interaction is parasitism: an interaction in which one organism (the parasite) benefits while the other (the host) is harmed.

    1 mark

Answer: A. The nematode would not mature or be transmitted. B. Selection favours nematodes that keep the host alive until a bird eats it. C. Parasitism: one benefits, the other is harmed.

Where the marks are

  • Early death prevents development and transmission (1 mark)
  • Selection favours nematodes that keep the ant alive until bird predation (1 mark)
  • Parasitism, correctly defined (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Organisms and Populations, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2026-27: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.