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Microbes in Human Welfare — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYMicrobes in Human Welfare1 Mark
Question
Two statements are given-one labelled Assertion and the other labelled Reason. Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both assertion and reason are true and reason is the correct explanation of assertion.
  2. Both assertion and reason are true but reason is not the correct explanation of assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false.
Assertion: Azolla is used as a biofertiliser in rice fields.
Reason: Azolla shows the presence of N2 - fixing bacteria in its leaf cavities.
✓

Answer

  1. Both assertion and reason are true and reason is the correct explanation of assertion.

Solution:

Azolla can co-exist with rice plants because it does not interfere with their growth. In some South East Asian countries, especially China, the rice fields are regularly provided with Azolla. The fem 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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