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Bio-fertilisers are… (Class 12 Biology SQP 2024-25, Q26)

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BiologyCBSE Class 12 · Sample paper, session 2024-25 · 3 marks · Short answer

CBSE Class 12 Biology sample paper 2024-25: question 26

From the official CBSE sample question paper for 2024-25, section C, question 26, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q26 · 3 marks · Short answerBiotechnology and its Applications

Bio-fertilisers are organisms that enrich the nutrient quality in the soil. Explain the role of three main sources of bio-fertilisers.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2024-25.

Hints

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

Hint 1

The three main groups are microbes: one bacterial, one fungal, one photosynthetic prokaryote.

Hint 2

Think of root nodules, root–fungus associations and paddy fields.

Hint 3

State which nutrient each group supplies.

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. Bacteria: Rhizobium lives symbiotically in the root nodules of leguminous plants and fixes atmospheric nitrogen into organic forms that the plant uses. Free-living bacteria such as Azospirillum and Azotobacter fix nitrogen in the soil and so enrich its nitrogen content.

    1 mark

  2. Fungi: Fungi form symbiotic mycorrhizal associations with plant roots, e.g. members of the genus Glomus. The fungus absorbs phosphorus from the soil and passes it to the plant. It also gives resistance to root-borne pathogens, tolerance to salinity and drought, and better overall growth.

    1 mark

  3. Cyanobacteria: These are autotrophic microbes, many of which fix atmospheric nitrogen, e.g. Anabaena, Nostoc and Oscillatoria. They are important biofertilisers in paddy fields and also add organic matter to the soil, increasing its fertility.

    1 mark

Answer: Bacteria (Rhizobium, Azotobacter, Azospirillum – nitrogen fixation), fungi (mycorrhiza/Glomus – phosphorus absorption), cyanobacteria (Anabaena, Nostoc – nitrogen fixation and organic matter in paddy fields).

Where the marks are

  • Role of bacteria in nitrogen fixation with examples (1 mark)
  • Role of mycorrhizal fungi in phosphorus uptake and other benefits (1 mark)
  • Role of cyanobacteria in nitrogen fixation and adding organic matter (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Biotechnology and its Applications, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2024-25: 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.