Question

Function of leghemoglobin during biological nitrogen fixation in root nodules of legumes is to
A. Convert atmospheric nitrogen to ammonia
B. Convert ammonia to nitrite
C. Transport oxygen for activity of nitrogenase
D. Protect nitrogenase from oxygen

Answer 1

The phenomenon of conversion of free nitrogen into nitrogenous salts to make it available for absorption by plants is called nitrogen fixation. The conversion of atmospheric nitrogen into organic and inorganic usable forms through the agency of living organisms is called biological nitrogen fixation.

Complete step by step answer: One of the most important nitrogen-fixing bacteria- Rhizobium fixes nitrogen in symbiotic association with roots of leguminous plants. Initially, the bacteria grow in the soil near the roots of higher plants where they fail to fix nitrogen. These bacteria come in contact with the roots of leguminous plants, interact chemically, and enter into the root hair depending on various chemical signals sent from the root hair. The enzymes from the bacteria degrade the parts of the root hair cell wall which produces a thread-like structure called infection thread. The bacteria multiply and invade the infection thread. Finally, the invading bacteria reach up to the inner cortex where they enter into cells and stimulate them to divide the proliferating cells are called root nodules. The bacteria multiply and colonize inside the tetraploid cells until the available cytosol is filled. They then become dormant. Each enlarged non-motile is called a bacteroid. A typical root nodule cell has several thousand bacteroids. Usually, the bacterium occurs inside the cytoplasm in groups. Each group of bacteroids is surrounded by a membrane called the peribacteroid membrane. The space around the peribacteroid membrane is called peribacteroid space. A red pigment leghaemoglobin is filled outside the peribacteroid space in the cytosol of nodule cells. The pigment of leghaemoglobin is similar to the haemoglobin of red blood cells. It has the ability to combine very rapidly with oxygen and thus acts as a very efficient oxygen scavenger. The enzyme nitrogenase is highly sensitive to molecular oxygen as it acts under anaerobic conditions. Due to which leghaemoglobin acts as an oxygen scavenger.
So, the correct answer is option D, i.e., Protect nitrogenase from oxygen

Note: Nitrogen so fixed is converted to nitrates and then to ammonia. Biological nitrogen fixation is also called associative symbiotic nitrogen fixation. They are of two types: symbiotic biological nitrogen fixation and biotic biological nitrogen fixation. Leguminous plants have a symbiotic association with the nitrogen-fixing bacteria