Which of the following pairs is a symbiotic nitrogen fixer in leguminous plants?
A. Rhizobium - Soybean
B. Frankia - Casuarina
C. Anabaena - Azolla
D. Azotobacter - Wheat
Answer: Option A
Solution (By JKSSB Mock Tests)
Rhizobium species form root nodules in leguminous plants like soybean, pea, and bean, where they fix atmospheric nitrogen symbiotically. Azotobacter is free-living, Anabaena associates with Azolla (a fern), Frankia with non-leguminous plants like Casuarina and Alnus. This symbiosis reduces the need for nitrogen fertilizers in agriculture.
Explanation:
Vitamin A (retinal) combines with opsin to form rhodopsin, the visual pigment in rod cells for dim-light vision. Deficiency causes night blindness.
Explanation:
Vitamin D (calcitriol) stimulates the production of calcium-binding proteins in the intestinal lining, enhancing calcium absorption. Deficiency leads to rickets/osteomalacia. Vitamin A is for vision, C for collagen, B₁₂ for nerve function.
Explanation:
Phycoerythrin absorbs blue-green light, which penetrates deeper water, allowing red algae to photosynthesize at greater depths. Fucoxanthin is in brown algae, chlorophyll b green, carotenoids orange.
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