The pigment that is the primary electron donor in photosystem I is: MCQ with Answer and Explanation

Explanation:
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:
Zinc is a component of the insulin hexamer stored in pancreatic beta cells; it stabilizes the insulin structure. Iron is in hemoglobin, calcium in bones/signaling, sulfur in some amino acids. Zinc deficiency impairs insulin secretion. Many enzymes require zinc as a cofactor.

Explanation:
Frederick Griffith in 1928 demonstrated the transformation of non-virulent pneumococci to virulent by heat-killed virulent strain, suggesting a transforming principle. Avery et al. later identified it as DNA. Hershey-Chase confirmed DNA is genetic material.