Which of the following statements about fermentation is correct? MCQ with Answer and Explanation

Explanation:
Biological nitrogen fixation, performed by bacteria (Rhizobium, Azotobacter) and cyanobacteria, reduces N₂ to NH₃. Nitrification oxidizes ammonia to nitrates, denitrification returns N₂, ammonification releases ammonia from organic matter.

Explanation:
Biotin is a coenzyme for carboxylation enzymes, including pyruvate carboxylase (gluconeogenesis) and acetyl-CoA carboxylase (fatty acid synthesis). Thiamine (B₁) is for decarboxylation, riboflavin (B₂) for redox, folate (B₉) for one-carbon transfers. Biotin is often bound to lysine in enzymes.

Explanation:
The tricuspid valve (right atrioventricular valve) has three cusps and closes during ventricular systole to prevent regurgitation into the right atrium. The bicuspid (mitral) is on the left side. Aortic and pulmonary valves are semilunar valves at the ventricular outlets.