Which of the following is a defining characteristic of meiosis? MCQ with Answer and Explanation

Explanation:
Vitamin B₁ (thiamine) is water-soluble and functions as a coenzyme (thiamine pyrophosphate) in carbohydrate metabolism, particularly in decarboxylation reactions. Vitamins A, D, E, and K are fat-soluble. B₁ deficiency causes beriberi and Wernicke-Korsakoff syndrome. Being water-soluble, excess is excreted in urine and toxicity is rare.

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:
Fleming accidentally discovered penicillin in 1928 when a mold contaminant (later identified as Penicillium notatum/now Penicillium chrysogenum) inhibited bacterial growth. This led to the first widely used antibiotic. Aspergillus species produce some toxins and acids, Saccharomyces is yeast, Agaricus bisporus is the common mushroom. Penicillin acts by disrupting bacterial cell wall synthesis.