The pacemaker of the human heart is the: MCQ with Answer and Explanation

Explanation:
Biological nitrogen fixation, carried out by symbiotic (Rhizobium) and free-living (Azotobacter) bacteria, reduces atmospheric N₂ to ammonia. Nitrification converts ammonia to nitrates, denitrification returns N₂ to air, ammonification releases ammonia from organic matter.

Explanation:
Megaloblastic anemia is characterized by large, immature RBCs due to impaired DNA synthesis from B₁₂ or folate deficiency. Microcytic is iron deficiency, sickle cell is genetic.

Explanation:
The stomach secretes gastric juice containing hydrochloric acid and the enzyme pepsin, which initiates the digestion of proteins into smaller peptides. The small intestine is the primary site for the final digestion of food and the absorption of most nutrients (amino acids, simple sugars, fatty acids, vitamins) into the bloodstream through its villi. The large intestine (colon) primarily absorbs water, electrolytes, and some vitamins produced by gut bacteria, forming solid feces. All statements are correct.