Answer: Cysteine and methionine.
- A Cysteine and methionine
- B Glycine and alanine
- C Valine and leucine
- D Serine and proline
Correct answer: A. Cysteine and methionine
Explanation: Sulphur is part of the amino acids cysteine and methionine, and of several vitamins and coenzymes.
Atmospheric N₂ is fixed into ammonia by nitrogen-fixing bacteria (protected from oxygen by leghaemoglobin in root nodules), converted to nitrate via nitrification for plant uptake, and eventually returned to the atmosphere as N₂ via denitrification, completing the cycle.
Concept context
Essential mineral elements, their roles and deficiency symptoms. Nitrogen fixation and soil nutrition.