Answer: Phosphorus.
- A Nitrogen
- B Sulfur
- C Potassium
- D Phosphorus
Correct answer: D. Phosphorus
Explanation: Phosphorus is a key component of ATP (energy), DNA/RNA (genetic material), and phospholipids (cell membranes). Deficiency causes poor root growth, purple discoloration of leaves, and delayed maturity.
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.