The symbiotic nitrogen-fixing cyanobacterium that lives in Azolla leaves is:
A. Rhizobium
B. Nostoc
C. Anabaena azollae
D. Azotobacter
Answer: Option C
Solution (By JKExamLibrary)
Anabaena azollae is a heterocystous cyanobacterium that lives symbiotically in the dorsal leaf cavities of the water fern Azolla. It fixes atmospheric nitrogen, providing a natural nitrogen source for rice paddies when Azolla is used as green manure. Nostoc is free-living or lichen symbiont, Rhizobium and Azotobacter are bacteria.
Explanation:
Chlorophyll a is the primary photosynthetic pigment, essential for converting light energy into chemical energy. It directly participates in the light reactions. Chlorophyll b, carotenes, and xanthophylls are accessory pigments that capture additional wavelengths and transfer energy to chlorophyll a. These accessory pigments also protect chlorophyll from photo-oxidation.
Explanation:
Tetanus (lockjaw) is caused by a neurotoxin produced by Clostridium tetani, which enters through wounds and causes painful muscle spasms. Botulism is C. botulinum, gas gangrene C. perfringens, leprosy M. leprae.
Explanation:
Adenylyl cyclase converts ATP to cyclic AMP, a second messenger. Guanylyl cyclase makes cGMP, phospholipase C produces IP₃/DAG, PKA is activated by cAMP.
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