Assertion: Oxygenic photosynthetic bacteria (cyanobacteria) generate oxygen as a by-product of photosynthesis, yet some are able to fix nitrogen as well.
Reason: These are colonial bacteria that have specialized cells (heterocysts) that lack the oxygen generating steps of photosynthesis.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false.

1. If both the assertion and the reason are true and the reason is a correct explanation of the assertion
2. If both the assertion and reason are true but the reason is not a correct explanation of the assertion
3. If the assertion is true but the reason is false
4. If both the assertion and reason are false

Assertion: The mutualistic association between the fern Azolla and the cyanobacterium Anabaena azollae is important agriculturally.
Reason: The water fern Azolla harbouring Anabaena is an important green manure for rice culture.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false.

Assertion: Elevated nitrate in groundwater is a concern for drinking water use.
Reason: Due to their very high solubility and because soils are highly unable to retain anions, nitrates can enter groundwater.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false.

Assertion: Denitrification is the oxidation of nitrates back into nitrogen gas (N₂).
Reason: This process is performed by bacterial species such as Pseudomonas and Clostridium in aerobic conditions.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false.

Assertion: Plant symbiont in Ectomycorrhizal mutualistic relationship form extensive root hair.
Reason: Ectomycorrhizas form between fungi and the roots of around 80% of plant species.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false.

Assertion: Arbuscular Mycorrhizal are facultative symbionts.
Reason: These fungi have extensive saprobic capabilities.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false.

Assertion: Carnivory is an evolutionary last resort when nitrogen and phosphorus are limited in an ecosystem.
Reason: Large amount of energy and resources are allocated to carnivorous adaptations.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false.

An element that is labeled as ‘essential’ for plants is characterized by all the following except:
1. Its deficiency cannot be met by supplying some other element
2. It allows normal vegetative growth but does not allow seed set, if absent
3. Its requirement must be specific
4. It must be directly involved in the metabolism of the plant

The minimum amount of requirement for an element to be classified as a macronutrient for plants is:
1. 5 mmole ${\mathrm{kg}}^{-1}$ of dry matter
2. 10 mmole ${\mathrm{kg}}^{-1}$ of dry matter
3. 20 mmole ${\mathrm{kg}}^{-1}$ of dry matter
4. 40 mmole ${\mathrm{kg}}^{-1}$ of dry matter

Which of the following element required by the plants is a micronutrient?