Answer: Boron cross-links pectin (as borate-diol ester) in the primary cell wall, maintaining wall integrity and cell-to-cell adhesion.
- A Boron functions as a major structural polymer that progressively displaces most of the cellulose normally found in the wall
- B Boron cross-links pectin (as borate-diol ester) in the primary cell wall, maintaining wall integrity and cell-to-cell adhesion
- C Boron deposits as a waxy cuticle layer across the wall surface, making it largely resistant to water loss over time
- D Boron contributes minimally to cell wall structure, playing a much smaller physiological role than calcium or magnesium
Correct answer: B. Boron cross-links pectin (as borate-diol ester) in the primary cell wall, maintaining wall integrity and cell-to-cell adhesion
Explanation: Boron forms borate ester bonds that cross-link rhamnogalacturonan II (RG-II) in the pectin fraction of primary cell walls. This borate-RG-II complex is essential for wall architecture and porosity. Boron deficiency disrupts pollen germination (borate needed for pollen tube growth) and causes death of growing tips.
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.