Mineral Nutrition Question 33
33. The product(s) of reaction catalyzed by nitrogenase in root nodules of leguminous plants is/are
[2020]
(a) Nitrate alone
(b) Ammonia and oxygen
(c) Ammonia and hydrogen
(d) Ammonia alone
Show Answer
Answer : c
Hints & Solution
(c) Ammonia and Hydrogen.
$N_2+8 e^{-}+8 H^{+}+16 ATP \to 2 NH_3+H_2$ $+16 ADP+16 Pi$
The steps involved in the process of nitrogen fixation are as follows:
- Rhizobia multiply and colonise the surroundings of roots and get attached to epidermal and root hair cells.
- The root-hairs curl and the bacteria invade the root-hair.
- An infection thread is produced carrying the bacteria into the cortex of the root, where they initiate the nodule formation in the cortex of the root.
- Then the bacteria are released from the thread into the cells which leads to the differentiation of specialised nitrogen fixing cells.
- The nodule thus formed, establishes a direct vascular connection with the host for exchange of nutrients.
- The nodule contains all the necessary biochemical components, such as the enzyme nitrogenase and leghaemoglobin.
The enzyme nitrogenase is a Mo-Fe protein and catalyses the conversion of atmospheric nitrogen to ammonia, the first stable product of nitrogen fixation. The enzyme nitrogenase is highly sensitive to the molecular oxygen; it requires anaerobic conditions. The nodules have adaptations that ensure that the enzyme is protected from oxygen. To protect these enzymes, the nodule contains an oxygen scavenger called leg-haemoglobin.
