The 'Hormone Calcitonin' is secreted by the parafollicular cells (C cells) of the thyroid gland and primarily acts to: MCQ with Answer and Explanation

Explanation:
Elephantiasis, or lymphatic filariasis, is caused by parasitic nematode worms, primarily Wuchereria bancrofti (responsible for about 90% of cases), Wuchereria malayi, and Brugia timori. These worms are transmitted by mosquitoes (like Culex). The adult worms lodge in the lymphatic vessels, causing severe inflammation, blockage, and damage to the lymphatic system. This leads to the accumulation of lymph fluid and massive, disfiguring swelling (edema) of the limbs, genitals, and breasts, resembling an elephant's skin and legs.

Explanation:
BCG (Bacille Calmette-Guérin) is a live attenuated vaccine derived from Mycobacterium bovis, used to protect against tuberculosis, especially in children. DPT is for diphtheria, pertussis, tetanus; MMR for measles, mumps, rubella; OPV is oral polio vaccine. BCG is often administered at birth in endemic regions.

Explanation:
Nitrogen fixation is the process by which atmospheric N₂ is reduced to ammonia, which is then converted into nitrates that plants can absorb. This can be biological (by bacteria like Rhizobium, Azotobacter), physical (lightning), or industrial (Haber-Bosch process). Nitrification is the oxidation of ammonia to nitrates. Ammonification releases ammonia from organic matter. Denitrification converts nitrates back to N₂.