Answer: Hydroponics.
- A Aeroponics
- B Drip irrigation
- C Hydroponics
- D Vermiculture
Correct answer: C. Hydroponics
Explanation: Hydroponics is the technique of growing plants in defined nutrient solutions without soil. It was used by scientists (Knop, Arnon) to discover which mineral elements are essential for plant growth.
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.