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Answer the following. (Class 12 Biology 2026, Q33b)

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BiologyCBSE Class 12 · Board exam 2026, set 57/1/1 · 5 marks · Long answer

CBSE Class 12 Biology 2026: question 33(b)

Set in the CBSE Class 12 board exam of 2026, paper 57/1/1, section E, question 33(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q33(b) · 5 marks · Long answerMicrobes in Human Welfare

Answer the following.

  1. (i)

    What are bio-fertilizers ?

    1 mark
  2. (ii)

    Name the different types of microorganisms used as bio-fertilizers in organic farming and explain how each contributes to soil fertility.

    3 marks
  3. (iii)

    Write two advantages of using bio-fertilizers over chemical fertilizers.

    1 mark

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 57/1/1.

Hints

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

Hint 1

Bio-fertilisers come from three groups of microbes.

Hint 2

Link each group to nitrogen fixation or phosphorus uptake.

Hint 3

Compare their environmental effects with those of chemical fertilisers.

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. (i) Bio-fertilisers are living organisms that enrich the nutrient quality of the soil. The main sources are bacteria, fungi and cyanobacteria.

    1 mark

  2. (ii) Bacteria.

    • Rhizobium forms a symbiotic association with the root nodules of leguminous plants and fixes atmospheric nitrogen into organic forms the plant can use.
    • Azotobacter and Azospirillum fix nitrogen while living freely in the soil.
    1 mark

  3. (ii) Fungi. The genus Glomus forms mycorrhiza with plant roots. The fungus absorbs phosphorus from the soil and passes it to the plant. Such plants also resist root-borne pathogens, tolerate salinity and drought, and show better growth.

    1 mark

  4. (ii) Cyanobacteria. Anabaena, Nostoc and Oscillatoria are autotrophic microbes that fix atmospheric nitrogen. They are important bio-fertilisers in paddy fields and also add organic matter to the soil.

    1 mark

  5. (iii) Any two advantages over chemical fertilisers:

    • They do not pollute the soil or groundwater.
    • They conserve beneficial soil microbes.
    • They do not contaminate food or harm human health.
    1 mark

Answer: (i) Organisms that enrich soil nutrient quality; (ii) bacteria (Rhizobium symbiotic, Azotobacter free-living N-fixation), fungi (Glomus mycorrhiza – phosphorus absorption), cyanobacteria (Anabaena/Nostoc – N-fixation in paddy fields); (iii) eco-friendly/no pollution; conserve soil microbes and are safe for health

Where the marks are

  • Defines bio-fertilisers (1 mark)
  • Names bacteria with their nitrogen-fixing role (½ + ½ marks)
  • Names fungi/Glomus with the mycorrhizal phosphorus-uptake role (½ + ½ marks)
  • Names cyanobacteria with their nitrogen-fixing role in paddy fields (½ + ½ marks)
  • Gives two advantages over chemical fertilisers (½ + ½ marks)

Revise the chapter

Practise this chapterBoard-style questions from Microbes in Human Welfare, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 57/1/1: 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.