6. Vitamin B₁₂ (Cobalamin) is only synthesized by

A. fishes
B. micro-organisms
C. plants
D. animals

7. Which of the following are reduced coenzymes?

A. NADH and FADH2
B. NAD⁺ and FAD
C. ATP and GTP
D. Coenzyme A and ubiquinone

8. The absence of ascorbic acid in the human diet gives rise to

A. rickets
B. pernicious anemia
C. cataract
D. beri-beri

9. Vitamins are essential because the organism

A. can’t synthesize these compounds at all
B. can synthesize these compounds partially
C. can’t synthesize these compounds in the adequate amounts
D. none of the above

10. The prosthetic group biotin is a carrier of which type of molecule?

A. Activated carbon dioxide (CO₂)
B. Ammonia
C. Methyl group
D. Sulfhydryl group