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MODEL PAPER 2 — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYMODEL PAPER 21 Mark
MCQ
Assertion (A): Azolla is used as a biofertiliser in rice fields.
Reason (R): Azolla shows the presence of N2 - fixing bacteria in its leaf cavities.
  • A
    Both A and R are true and R is the correct explanation of A
  • B
    Both A and R are true but R is not the correct explanation of A.
  • C
    A is true but R is false.
  • D
    A is false but R is true.
✓

Answer

Both A and R are true and R is the correct explanation of A.
Explanation: Azolla can co-exist with rice plants because it does not interfere with their growth. In some southeast Asian countries, especially China, the rice fields are regularly provided with Azolla. The fern is stocked in a corner of rice field and provided with manure, ash, and straw before transplantation. When the field is flooded at the time of transplantation, the fern spreads rapidly and covers the space in between the rice plants. Anabaena, a blue-green algae resides in the leaf cavities of the fern, It fixes nitrogen. A part of the fixed nitrogen is excreted in the cavities and becomes available to the fern. The decaying fern plants release the same for utilisation by the rice plants.

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