Answer: A pink oxygen-scavenging protein in root nodules that maintains anaerobic conditions for nitrogenase.
- A A plant growth hormone that specifically triggers rapid cell division within the root cortex tissue
- B A pink oxygen-scavenging protein in root nodules that maintains anaerobic conditions for nitrogenase
- C A carbohydrate storage compound that holds fixed nitrogen in the form of starch granules
- D A diffusible signal protein released by Rhizobium that specifically triggers root hair curling
Correct answer: B. A pink oxygen-scavenging protein in root nodules that maintains anaerobic conditions for nitrogenase
Explanation: Leghemoglobin is a pink/red protein found in legume root nodules. It scavenges free O<sub>2</sub> in the nodule, maintaining the anaerobic microenvironment required by nitrogenase (which is O<sub>2</sub>-sensitive). Its genes come from both the plant and Rhizobium.
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.